Adaptive synchronization arrangement

ABSTRACT

A CDMA cellular radio-telephone system (FIG. 2) has switching systems (201) synchronized to public telephone network (100) timing signals (600), and radio telephones (203) and cell base stations (202) synchronized to different clock (1000). Transmission delays between the cell base stations and the telephone network are variable. Switching systems include digital communications interfaces (264) to the telephone system, whose connections to the telephone system are synchronized to the telephone system, and whose connections to the cells are nominally also synchronized to the telephone system but whose processor (602) operates for each call within predefined windows (1302, 1402) of phase relationships to the operation of the cell that is handling the call, and occasionally adjusts (FIGS. 13-16) its phase relationships to the operation of the telephone system to achieve and maintain its operation within the predefined windows. Packet-switched communications (350) between the cells and the switching systems absorb the phase relationship fluctuations and the timing adjustments in inter-packet intervals. Circuit-switched digital communications between the switching systems and the telephone system absorb the timing adjustments by means of vocoder (604)-implemented slips--bit insertions or deletions--in the communications traffic bit stream.

CROSS-REFERENCE TO RELATED APPLICATIONS

B. D. Bolliger, T. P. Bursh, Jr., M. K. Dennison, M. J. English, C. Y.Farwell, M. L. Hearn, R. M. Heidebrecht, K. K. Ho, K. Y. Ho, D. M.Kissel, P. E. Miller, R. D. Miller, A. S. Mulberg, L. N. Roberts, M. A.Smith, K. F. Smolik, D. A. Spencer, K. W. Strom, and J. S. Thompson, andR. A. Windhausen, "Wireless Access Telephone-to-Telephone NetworkInterface Arrangement", Ser. No. 07/727,498 filed on even date herewithand assigned to the same assignee;

C. Y. Farwell, M. L. Hearn, R. M. Heidebrecht, K. K. Ho, and D. A.Spencer, "Adaptive Synchronization Arrangement", Ser. No. 07/727,492filed on even date herewith and assigned to the same assignee; and

B. D. Bolliger, T. P. Bursh, Jr., K. K. Ho, A. S. Mulberg, L. N.Roberts, K. F. Smolik, D. A. Spencer, K. W. Strom, and J. S. Thompson,"Mobile Telephone System Call Processing Arrangement", Ser. No.07/727,520 filed on even date herewith and assigned to the sameassignee.

TECHNICAL FIELD

This invention relates generally to network-independent timingarrangements, and relates specifically to digital radio-telephonyarrangements wherein operations of the telephone network and the radionodes are synchronized to different clocks.

BACKGROUND OF THE INVENTION

It sometimes occurs in digital telecommunications systems thatcustomer-premises communications equipment is timed independently of thenetwork communications equipment (e.g., the public switched telephonynetwork) that interconnects the customer-premises equipment. Aparticularly significant example thereof is the code-divisionmultiplexed-access (CDMA) radio-telephone system, which is an importanttype of digital cellular mobile-telephone system. In the CDMA system,nodes that contain radios, i.e., the mobile radio-telephones andcell-site base stations (cells for short), are synchronized to clocksignals received by the cells from a global-positioning system (GPS)satellite, whereas the radio-telephone switching systems whichinterconnect the base stations with each other and with the publictelephone network by means of digital communications are synchronized toclock signals which may also be received from the GPS satellite but aredistributed by the telephone network.

For purposes of this discussion, two series of events, signals, oroperations are considered to be synchronized with each other, orsynchronous, if (a) they either occur at the same nominal frequency orone occurs at a frequency that is an integral multiple of the frequencyof the other, and (b) they occur in a fixed phase relationship with oneanother. Operations that are not synchronous are considered to beasynchronous for purposes of this discussion.

The independent timing of the operation of different units of acommunication system destroys the assumption that the units provide calltraffic to each other at a predetermined steady and unvarying frequencyat steady and unvarying points in time i.e. a fixed phase. Rather,independent timing results in the units providing call traffic to eachother at a rate and at points in time that fluctuate about a fixedfrequency and phase. This asynchrony must be compensated for somehow.

Independent timing is but one cause of this asynchrony. Another causethat may be present in communication systems, such as the CDMAradio-telephone system mentioned above, is the lack of a predeterminedand fixed transmission delay between the communicating units. Assumingthat both the originating and the destination units are timed either bya common clock or by different clocks that are synchronized with eachother, if the transmission delay between the units is fixed andpre-determinable, it can be compensated for in the communication systemdesign such as to allow the units to operate synchronously with eachother. But if the delay cannot be predetermined but is variable andfluctuates, the net effect is the same as if the units wereindependently timed. The fluctuation in the delay may be a result of,for example, occasional changes in the transmission paths that arefollowed by communications moving between communicating units, orvariances in the communication traffic load that flows between--and thatmust be handled by--the communicating units. This asynchrony mustlikewise be compensated for.

A partial though inadequate solution to the problems caused byindependent timing is to conduct communications between thecommunicating units in analog instead of digital form. Analogcommunications can be received asynchronously with their transmission.And while the asynchrony may introduce errors or "glitches" into thecommunications, the problem is often tolerable for voice-onlycommunications. Thus, in the CDMA radio-telephone system, theradio-telephone switching systems may also be synchronized to the GPSsatellite clock signals and hence operate synchronously with theradio-telephones and base stations, if the switching systems areinterfaced to the telephone network via analog voice-onlycommunications. Of course, such an arrangement suffers all of thedisadvantages that are associated with analog communications, such aslow quality and capacity and susceptibility to interference, plus theproblem of asynchrony-induced glitches that make the arrangementunsuitable for data communications.

Likewise, a partial though inadequate solution to the problems caused byfluctuating transmission delays is to circuit-switch communicationtraffic, whereby the dependency of transmission delay on communicationtraffic load is avoided. However, circuit-switching is inefficient orundesirable for other reasons in many applications. Furthermore, circuitswitching does not eliminate fluctuation of transmission delay that iscaused by changes in the transmission path, such as will typically ariseduring CDMA call "soft handoff".

SUMMARY OF THE INVENTION

This invention is directed to solving these and other disadvantages ofthe prior art. Broadly according to the invention, in a digitaltelecommunication system having independently-timed units, there isprovided an interface between the asynchronously-operating units whichis nominally synchronized with ones of the units but which operateswithin a predefined window, i.e., a range, of phase relationships to theoperation of the others of the units and occasionally adjusts itsotherwise-fixed phase relationaship wih the operation of the ones of theunits to achieve and maintain its operation within the predefinedwindow. The asynchronous operations of the various units therebyeffectively become synchronized with the operations of the interfacearrangement, and thus are able to proceed substantially as if they weresynchronized with each other.

The use of the invention is not limited to digital telecommunicationssystems, but extends to any apparatus that includes a first operatingunit having its operations synchronized with first clock signals and asecond operating unit having its operations synchronized with secondclock signals which are asynchronous with the first clock signals andwherein the operations of the two units need to be interfaced. Accordingto the invention, such an apparatus includes a third operating unit forinterfacing the operations of the first unit with the operations of thesecond unit, which has its operations nominally synchronized with theoperations of the first unit. Furthermore, the extent of asynchronybetween the operations of the second and the third units is monitored todetermine whether the extent of asynchrony lies outside of apredetermined range of allowed asynchrony. If so, the synchronization(e.g., the phase relationship) of the operations of the third unit withthe operations of the first unit is adjusted so as to move the extent ofasynchrony between the operations of the second and the third unitswithin the allowed range.

Specifically according to the invention, in a CDMA radio-telephonesystem, each radio-telephone switching system includes a digitalcommunications interface arrangement whose connections to the telephonesystem are synchronized to the operation of the telephone system, andwhose connections to the base stations (cells) are nominally alsosynchronized to the operation of the telephone system but which operatesfor each individual call within a predefined window of phaserelationships to the operation of the base station that is handling thecall and occasionally adjusts its phase relationship with the operationof the telephone system to achieve and to maintain its operation withinthe predefined window. According to an illustrative embodiment, theinterface arrangement utilizes message-based, e.g., packet-switched,communications between the base stations and the switching system,wherein the phase relationship fluctuations and the timing adjustmentsare absorbed by variations in inter-message intervals. Further accordingto an illustrative embodiment, the interface arrangement utilizescircuit-switched communications between the switching system and thetelephone network, wherein the timing adjustments are absorbed byslips--bit duplications or deletions--in the communications bit stream.

The asynchronous operation of the various system units is therebycompensated for and accommodated by the interface arrangement, asrequired for proper digital communications system operation.

While the discussion of an illustrative embodiment that follows makes adistinction between level-3 "packet" and level-2 "frames", for purposesof clarity, the use of the term "packet" herein and in the claims isintended to encompass either or both "packets" and "frames".

These and other advantages and features of the invention will becomeapparent from the following description of an illustrative embodiment ofthe invention considered together with the drawing.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a block diagram of a conventional cellular radio-telephonesystem;

FIG. 2 is a block diagram of a cellular radio-telephone system thatincorporates an illustrative embodiment of the invention;

FIG. 3 is a block diagram of a cell of the system of FIG. 2;

FIG. 4 is a block diagram of a cell interconnect module of the system ofFIG. 2;

FIG. 5 is a block diagram of a speech coding module of the system ofFIG. 2;

FIG. 6 is a block diagram of a speech processing iunit of the module ofFIG. 5;

FIG. 7 is a block diagram of a LAPD frame of the system of FIG. 2;

FIG. 8 is a block diagram of a modified LAPD frame of the system of FIG.2;

FIG. 9 is a block diagram of a level-3 protocol used for carrying voiceand/or signalling information in the frames of FIGS. 7 and 8;

FIG. 10 is a block diagram of a level-3 protocol used for carryingsignalling information in the frames of FIGS. 7 and 8;

FIGS. 11-14 are a flow diagram of received-packet processing functionsof the processor of the unit of FIG. 6;

FIG. 15 is a flow diagram of transmit-packet processing functions of theprocessor of the unit of FIG. 6;

FIG. 16 is a flow diagram of clock adjustment functions of a clustercontroller of the cell of FIG. 3;

FIG. 17 is a flow diagram of clock adjustment functions of the processorof the unit of FIG. 6 performed at step 970 of FIG. 11;

FIG. 18 is a flow diagram of clock adjustment functions of the processorof the unit of FIG. 6 performed at step 912 of FIG. 11;

FIG. 19 is a timing diagram of packet-transmission clock-adjustmentsperformed at call setup for a service circuit of the unit of FIG. 6;

FIG. 20 is a timing diagram of packet-reception clock-adjustmentsperformed at call setup for a service circuit of the unit of FIG. 6;

FIG. 21 is a timing diagram of packet-transmission clock-adjustmentsperformed during an established call for a service circuit of the unitof FIG. 6;

FIG. 22 is a timing diagram of packet-reception clock-adjustmentsperformed during an established call for a service circuit of the unitof FIG. 6;

FIG. 23 is a signalling diagram of setup of a mobile-originated call inthe system of FIG. 2;

FIG. 24 is a signalling diagram of setup of a network-originated call inthe system of FIG. 2;

FIG. 25 is a signalling diagram of a mobile-originated disconnection ofa call in the system of FIG. 2;

FIG. 26 is a signalling diagram of a network-originated disconnection ofa call in the system of FIG. 2;

FIG. 27 is a signalling diagram of the beginning of a soft-handoff of acall in the system of FIG. 2;

FIG. 28 is a signalling diagram of the end of a soft-handoff wherein amaster cell drops off;

FIG. 29 is a signalling diagram of the end of a soft-handoff wherein aslave cell drops off;

FIG. 30 is a signalling diagram of a mobile-originated disconnection ofa call during soft-handoff in the system of FIG. 2;

FIG. 31 is a signalling diagram of a network-originated disconnection ofa call during soft-handoff in the system of FIG. 2;

FIG. 32 is a signalling diagram of a semi-soft-handoff of a call in thesystem of FIG. 2;

FIG. 33 is a signalling diagram of a CDMA-to-CDMA hard-handoff of a callin the system of FIG. 2;

FIG. 34 is a signalling diagram of a CDMA-to-analog hard-handoff of acall between cells served by the same digital cellular switch in thesystem of FIG. 2; and

FIG. 35 is a signalling diagram of a CDMA-to-analog hard-handoff of acall between cells served by different digital cellular switches in thesystem of FIG. 2.

DETAILED DESCRIPTION

Before commencing a discussion of an illustrative implementation of theinvention, it may be helpful to consider an existing cellular mobileradio-telephone system to serve as a basis for comparison. Such a systemis shown in FIG. 1. A description of such a system may be found K. W.Strom, "On the Road with AUTOPLEX System 1000", AT&T Technology, Vol. 3,No. 3, 1988, pp. 42-51, and W. J. Hardy and R. A. Lemp, "New AUTOPLEXCell Site Paves The Way For Digital Cellular Communications", AT&TTechnology, Vol. 5, No. 4, 1990, pp. 20-25.

The system of FIG. 1 includes a plurality of geographically-dispersedservice nodes known as cell sites, or cells 102 for short, each one ofwhich provides radio-telephone services to wireless user terminals,known as mobile radio-telephones 103, in its vicinity. To provideradio-telephone service between mobile radio-telephones 103 served bydifferent cells 102, and between mobile radio-telephones 103 and thepublic telephone network 100, cells 102 are interfaced to each other andto network 100 through mobile radio-telephone switching nodes referredto herein as digital cellular switches (DCSs) 101. Each switch 101 isillustratively the AT&T Autoplex® cellular telecommunications systemdigital cellular switch. Each digital cellular switch 101 is connectedto a plurality of different cells 102 by communication trunks 107, andis connected to network 100 by communication trunks 106. Each trunk 106and 107 is illustratively a DS0(64 Kbps time-division multiplexed)channel, a plurality of which are implemented by a DS1 facility whichmay be transported via land line (T1 line), optical transmission,microwave, etc., facilities. Control over the system of FIG. 1 andcoordination of the activities of the various cells 102 and DCSs 101 isexercised by an Executive Cellular Processor (ECP) 105, which isconnected to each cell 102 and cellular switch 101 through anInterprocess-Message Switch (IMS) 104 by control links 108. ECP 105 andIMS 104 together make up an ECP complex 134. ECP complex 134 and DCS 101make up a mobile switching center (MSC) 199. ECP 105 and IMS 104 areillustratively the AT&T Autoplex ECP and the AT&T Autoplex IMS (whichincludes a plurality of cell site node processors, digital switch nodeprocessors, and database node processors, interconnected by an IMSring), and links 108 are illustratively RS-449 data links within MSC199. Alternatively, control links 108 may be implemented as 64 Kbps DS0channels on DS1 facilities between cells 102 and mobile switching center199.

Each mobile radio-telephone 103 typically comprises an analog FMradio-telephone capable of operating at any one of a plurality of radiofrequency pairs. Each cell 102 comprises a plurality of analog FM radios143 each operating at one of the radio frequency pairs of the mobileradio-telephones 103. Radios 143 of adjacent cells 102 operate atdifferent frequency pairs, to avoid interfering with each other.However, each mobile radio-telephone 103 is typically capable ofoperating at any of the frequency pairs of all of the cells 102.

In an alternative embodiment, digital radios and radio-telephonesoperating in time-division multiple-access (TDMA) mode are substitutedfor the analog FM radios and radio-telephones. Vocoding functions can bea part of the radio units in this embodiment, or can be located atswitches 101.

While in a cellular system, a mobile radio-telephone's receiver scans aset of predetermined paging channels. After locking onto the strongestpaging channel, the mobile radio-telephone 103 gets instructions fromthe system and receives incoming calls. A mobile radio-telephone 103also transmits on a channel to originate a call. When a call isestablished (incoming or outgoing) the receiver is assigned to aparticular voice channel and instructed to tune to that transmit andreceive frequency pair. At the same time, a connection is establishedbetween the cell 102 and the telephone network 100 through a digitalcellular switch 101, which completes the voice path for the telephoneconversation.

Once this voice connection is established, the radio signal levels aremonitored by the cell's radio 143. As the mobile radio-telephone 103moves from one cell into another, the serving cell 102 detects thereduction in signal strength and requests that measurements be made bysurrounding cells 102. If these measurements indicate that another cell102 can provide better service, then the voice connection is switched tothat cell 102 through a process known as "hard handoff". The process ofhard handoff is under control of ECP 105 and requires that a DCS 101first form a 3-way connection which extends the voice circuit from theserving trunk 106 to radio channels in both the serving cell 102 and thetarget cell 102. When this connection has been confirmed, theradio-telephone 103 is instructed to retune to the frequency of theassigned radio 143 in the target cell 102. Upon confirmation of theradio-telephone's communication with the target cell 102, the DCS 101 isthen instructed to remove the voice connection to the original servingcell 102, leaving the connection between the new serving (target) cell102 and the serving trunk 106. The telephone conversation continueslargely uninterrupted through this handoff process. Meanwhile, theoriginal voice channel is made available for use by another subscriber.

Hard handoffs performed in this way use processor capacity in both theECP complex 134 and the digital cellular switch 101. For the duration ofthe 3-way connection, the hard handoff also uses additional switchfabric (TDM bus 130) capacity. If the target cell 102 containing theselected radio 143 is connected to a switching module 120 other than theone containing the serving trunk 106, then the connection must beextended through a time-multiplexed switch (TMS) 121, using additionalswitching fabric in that switch element. As the number of cells 102 in asystem grows larger, the number of handoffs increases and uses anincreasing proportion of the system processor and switch fabricresources, thus reducing the system's overall capacity.

Each cell 102 is configured around a high-speed time-divisionmultiplexed (TDM) bus 140. TDM bus 140 is illustratively the 2.048 MHzTDM bus of an AT&T Definity® communications system Universal Module, andphysically comprises one or more TDM buses each having 256 time-slotsper frame. Illustratively, multiple TDM buses are used simultaneously byunits connected thereto and logically operate as a single TDM bus havinga multiple of 256 time-slots per frame. Each time slot has a rate of 64Kbps. Within a cell 102, radios 143 are connected to TDM bus 140. Radios143 accept communications for radio transmission from, and supplyreceived radio communications to, TDM bus 140 in DS0 channel format at arate of 64 Kbps. The input to, and output from, each radio is full-ratepulse-code-modulation (PCM)-coded speech. Also connected to TDM bus 140are one or more interfaces 142, each one of which couples TDM bus 140 totrunks 107. Illustratively, trunks 107 are carried by T1 facilitiesemploying the DS1 communication format and operating at a rate of 1.544Mbps, and so interfaces 142 are DS1 interfaces. The DS1 and theaforementioned DS0 format are described by T. H. Murray in "TheEvolution of DDS Networks: Part 1", Telecommunications, February 1989,pp. 39-47. An interface 142 accepts from TDM bus 140 communications thathave been supplied by a plurality of radios 143, multiplexes them intothe DS1 format, and transmits them onto trunks 107. In the reversedirection, interface 142 receives from trunks 107 communicationsformatted in the DS1 format, demultiplexes them, and supplies them toTDM bus 140 for conveyance to radios 143. TDM bus 140 operates undercontrol of a controller 141, which allocates time slots on bus 140 toindividual ones of the radios 143 and interfaces 142. Illustratively,controller 141 makes these allocations on the basis of controlinformation supplied thereto by ECP complex 134 over a control link 108;alternatively, controller 141 may have a database that allows it to makethe allocations autonomously.

Each digital cellular switch 101 comprises one or more digital switchingmodules (DSMs) 120. A module 120 structurally resembles a cell 102 inthat it comprises a TDM bus 130 which is similar to TDM bus 140, acontroller 131 which provides the same TDM bus control functions ascontroller 141, and a plurality of interfaces 132 connected to bus 130which provide the same functionality as interfaces 142. On the basis ofcontrol communications originating from ECP complex 134, controller 131causes communications to be switched by TDM bus 130 between interfaces132. Each trunk 107 extending from a cell 102 is terminated at aswitching module 120 by an interface 132. Other interfaces 132 at amodule 120 terminate trunks 106, which are duplicates of trunks 107 butextend to public telephone network 100.

If switch 101 includes more than one module 120, it also includes atime-multiplexed switch (TMS) 121. Then a TMS interface 133 is connectedto TDM bus 130 in each module 120 and terminates a link 109 whichextends to TMS 121. Interface 133 is illustratively the Module ControlComplex (MCC) of an AT&T Definity communications system UniversalModule. TMS 121 provides direct switched interconnection between modules120 of one mobile radio-telephone switch 101. Interconnection betweenmodules 120 of different mobile radio-telephone switches 101 is providedby public telephone network 100 or by trunks that interconnect switches101 directly.

Overall control of a digital cellular switch 101 and coordination ofactivities between its modules 120 and 121 is exercised by a DCScontroller 161. DCS controller 161 is in direct communication with ECPcomplex 134 over a control link 108. Controller 161 has its own controlconnection to TMS 121 through link 150, and to controllers 131 ofswitching modules 120 through link 150 and TMS interfaces 133.Controller 161 is illustratively the 501 CC processor of an AT&TDefinity communications system.

Turning now to FIG. 2, it shows an illustrative example of a cellularmobile radio-telephone system constructed according to the invention.Same numerical designations as were used in FIG. 1 are used in FIG. 2 todesignate elements that are common to both systems.

FIG. 2 shows a system topology that resembles the one of FIG. 1 in manyrespects, though it is not identical. The system of FIG. 2 includes aplurality of geographically-dispersed cells 202, each one of whichprovides radio-telephony services to mobile radio-telephones 203 in itsvicinity. As used herein, cell 202 refers either to a geographicallyseparate cell site or to one of a plurality of "faces" on a given cellsite, where a "face" is a cell sector as is typically implemented byusing directional transmit antennas at a cell site. The operation of allmobile radio-telephones 203 and cells 202 is synchronized to a commonmaster clock, such as to timing signals generated and broadcast by aglobal positioning system satellite. Interconnection between cells 202,and between cells 202 and public telephone network 100, is accomplishedby digital cellular switches 201, in two stages. First, individual cells202 are connected to one or more cell interconnect modules (CIMs) 209 ofa DCS 201 by trunks 207. Cell interconnect modules 209 of individualDCSs 201 are each in turn connected to each speech coding module (SCM)220 of that DCS 201 by fiber-optic packet-switched trunks 210. Digitalcellular switches 201 are each connected to public network 100 by aplurality of trunks 106, analogously to FIG. 1, and directly to eachother by trunks 206 that functionally duplicate trunks 106. Theoperation of switches 201 is synchronized to master timing signals (notshown) of public telephone network 100. Further analogously to FIG. 1,cells 202 and digital cellular switches 201 operate under control of ECPcomplex 134, to which they are connected by control links 108. Likewise,the various modules 209 and 220 of a DCS 201 are connected by controllinks 208 to a common DCS controller 261 and operate under its control.Physically, DCS controller 261 is illustratively again the 501 CCprocessor.

In the system of FIG. 2, some, but not necessarily all, mobileradio-telephones 203 are digital radio-telephones. While illustrativelyshown as mounted in a vehicle, a mobile radio-telephone 203 may be anyportable radio-telephone, and may even be a stationary radio-telephone.The digital radio-telephones use voice-compression techniques to reducethe required digital transmission rate over the radio channel. Eachdigital radio-telephone includes voice-compression circuitry in itstransmitter and voice-decompression circuitry in its receiver. Eachradio-telephone is capable of operating at any one of a plurality ofwideband radio frequency pairs.

For handling non-packetized traffic analogous to that handled by thesystem of FIG. 1, side-by-side with packetized traffic, a DCS 201 of thesystem of FIG. 2 includes the elements shown in dashed lines: a TMS 121connected by trunks 109 to modules 209 and 220, and trunks 106connecting CIMs 209 directly to public telephone network 100. Their useis enlightened further below.

Digital radio-telephones 203 may operate in one or more of time-divisionmultiple-access (TDMA) mode or code-division multiple-access (CDMA) modeor some other digital or analog radio mode. TDMA is a technique, knownin the art, that provides multiple users access to a radio channel(frequency) by dividing that channel into multiple time slots. A singleuser can be assigned to one or more of these time slots. A TDMA radio203 is illustratively the TIA IS54 digital cellular radio. TDMA employsdifferent frequencies in adjacent cells and therefore requires the "hardhandoff" procedure described previously.

In the present illustrative example, digital radio-telephones 203 areassumed to operate in CDMA mode, or as a fallback in the FDMA (analog)mode. CDMA is a direct-sequence spread-spectrum technique which allowsreuse of the frequencies in the territories served by adjacent cells202. Consequently, adjacent cells 202 need not, and do not, operate atdifferent radio frequencies, but re-use the same frequencies. Whenmoving from the vicinity of one cell 202 to the vicinity of another cell202, a mobile radio-telephone 203 may undergo a "hard handoff"procedure, described previously. However, a CDMA mobile radio-telephone203 in the system of FIG. 2 may alternatively and preferentially undergoa "soft handoff" procedure, during which it communicates with both ofthe cells 202 on the same frequency pair at the same time. The CDMAtechnique and its associated procedures and equipment are also known inthe art. The basic principle of direct-sequence code-divisionmultiple-access is the use of a plurality of individual and distincthigh-speed digital signals which are absolutely or statisticallyorthogonal to each other, each to modulate one of a plurality oflow-speed (i.e., baseband) user signals and to combine the plurality ofmodulated signals into common digital signals which then are used tocontrol radio frequency modulation functions. Recovery and separation ofthe original baseband signals is accomplished using the correspondingdigital modulation signals to demodulate within a time-synchronousmanner. For a description of CDMA see, e.g., U.S. Pat. No. 4,901,307,and published international patent applications WO 91/07020, WO91/07036, and WO 91/07037.

A cell 202 is shown in FIG. 3. Similarly to a cell 102 of FIG. 1, cell202 includes TDM bus 140 operating under control of controller 241, andDS1 interfaces 242 couple TDM bus 140 to trunks 207. Controller 241 isillustratively the control complex of an AT&T Autoplex Series II cellsite. It functionally duplicates controller 141 of a cell 102, but nowperforms additional functions, described below, on account of the factthat cell 202 comprises a plurality of digital radios 243. Every digitalradio's signal input and output are interfaced to TDM bus 140 bycorresponding one or more channel elements 245 and a cluster controller244. A channel element 245 is an interface to digital radios 243 servingan individual user. Channel elements 245 provide signal processingfunctions--baseband and spread-spectrum (CDMA) signal processingfunctions in this example--for individual calls being transmitted andreceived by their associated radios 243.

Each cluster controller 244 includes a C-bus 390. C-bus 390 isillustratively a conventional computer input and output (I/O) bus, andchannel elements 245 are connected to C-bus 390 as computer I/O devices.C-bus 390 and channel elements 245 operate under control of a controller393. Controller 393 is illustratively a general-purpose microprocessor,and it is served by a bus 391 which is illustratively a conventionalmicroprocessor main bus. Bus 391 is connected to C-bus 390 by a C-businterface 392 which functions as an I/O interface of conventionaldesign. Controller 393 orchestrates data movement between channelelements 245 and cell 202 TDM bus 140 (illustratively, one transfer ineach direction for each channel element 245 every 20 msecs.), performsoperation, administration, and maintenance (OA and M) functions oncluster controller 244, handles cell-site signalling and otherspecialized functions, and performs level-2 and level-3 protocolformatting and deformatting functions on data (call traffic andsignalling) passing between channel elements 245 and TDM bus 140. Amemory 394 is connected to bus 391 and serves as a scratch-padtraffic-buffer memory and an instruction memory for controller 393. Alsoconnected to bus 391 is an HDLC controller 395. It performs HDLCformatting and deformatting functions on traffic flowing between channelelements 245 and TDM bus 140, including traffic conversion betweenbyte-oriented form used in cluster controller 244 and bit-oriented formused on TDM bus 140, including bit stuffing and LAPD flag insertionfunctions. HDLC controller 395 receives and transmits HDLC serial bitstreams from/to TDM bus 140 through a TDM bus interface 396, ofconventional design, which connects controller 395 to bus 140.

Compressed call traffic and signalling are transported between channelelements 245 and cluster controller 244 in the form of segments ofbyte-oriented information. Each channel element 245 transmits andreceives a segment of byte-oriented information at regular intervals,illustratively every 20 msecs. Cluster controller 244 formats eachsegment of byte-oriented information in LAPD protocol format whichincludes a level-3 protocol, for transmission to DCSs 201. While anysuitable level-3 protocol may be used, illustrative level-3 protocols350 and 351 are shown in FIGS. 9 and 10.

FIG. 9 shows a protocol 350 that is used to convey either call trafficor signalling or both, while FIG. 10 shows a protocol 351 that isdedicated to conveying a particular type of signalling. Both protocols350 and 351 are carried by frames of FIGS. 7 and 8. A level-3 protocoldata unit carried over a level-2 protocol is commonly referred to as apacket, and a level-2 protocol data unit is commonly commonly referredto as a packet, and a level-2 protocol data unit is commonly referred toas a frame. Protocol 350 of FIG. 9 comprises at least the informationfields 320-327. Additional fields for other types of information may beincluded in packet 350, but these are not germane to the presentdiscussion. Sequence number field 320 carries a sequential number ofthis packet 350 within the sequence of packets transmitted in a givendirection. In the case of packet 350 outgoing to a channel element 245from a DCS 201, the sequence numbers begin at 0 at the start of everynew call. In the case of packets 350 incoming from a channel element 245to a DCS 201, the sequence numbers are derived from the master timingsignals to which all mobile telephones 203 and cells 202 aresynchronized. Packet type field 321 identifies the packet type as eithera traffic packet, corresponding to packet 350 of FIG. 9, or a signallingpacket, corresponding to packet 351 of FIG. 10. Clock adjust field 322carries information from cluster controllers 244 to DCSs 201 that isused to compensate for real and virtual drift between the master clockto which mobile telephones 203 and cells 202 are synchronized and amaster clock to which public telephone network 100 and DCSs 201 aresynchronized. Field 322 is used only in the reverse direction, and isnull in the forward direction. Air CRC field 323 is the result of aconventional check-sum, computed by a mobile telephone 203 over itstransmitted traffic, and is sent by mobile telephone 203 along with thattraffic. Signal quality field 324 carries reports computed by channelelements 245 on the quality of call-traffic signals that they arereceiving from mobile telephone 203. Fields 323 and 324 are also usedonly in the reverse direction and are null in the forward direction.Power control field 325 carries information from a cell 202 concerningthe trend of power control instructions sent by a channel element 245 toits corresponding mobile telephone 203. Normally, this field is alsoused only in the reverse direction, but is used in both directionsduring soft handoff, as will be explained further below.Voice/signalling type field 326 identifies the type of information thatis carried by packet 350: voice traffic only, voice plus signalling, orsignalling only. And voice/signalling data field 327 carries call voicetraffic or signalling information, or a mix of both, to and from channelelements 245.

A signalling packet 351, shown in FIG. 10, is simpler than trafficpacket 350 of FIG. 9: it has fields 321 and 328-331 that are relevant tothis discussion. Packet type field 321, already discussed in conjunctionwith FIG. 9, identifies packet 351 as a signalling packet. Message typefield 328 identifies the type of signalling carried by packet 351.Channel element ID field 329 identifies the particular channel element245 participating in this message exchange. Frame selector ID field 330identifies a particular virtual port on a processor 602 (see FIG. 6)participating in this message exchange. These fields 329 and 330 may beused for security, maintenance, performance tracking, billing, routing,etc. Channel element 245 and frame selector IDs are assignedadministratively at system configuration time, and remain fixedthereafter. And signalling data field 331 carries the signallinginformation that is being conveyed.

A cluster controller 244 couples a plurality of channel elements 245 toTDM bus 140. Each cluster controller 244 communicates on TDM bus 140through an allocated input and an output "pipe". The allocation isadministrable, and is typically done at system initialization. Each"pipe" illustratively constitutes a plurality of (e.g., four) time slots(i.e., four 64 Kbps channels) on TDM bus 140. In the reverse (inbound)direction, cluster controller 244 queues traffic segments received fromchannel elements 245, formats them into packets, wraps the packets intoinverted-HDLC-format LAPD (level-2 protocol) frames, and transmits theLAPD frames one after another into its allocated output "pipe" on TDMbus 140. In the forward (outbound) direction, cluster controller 244receives LAPD frames from its allocated input "pipe" on TDM bus 140,terminates the LAPD protocol, deformats the packets, and thendistributes the contents of these packets to channel elements 245according to an address field embedded in the received frames. As aconsequence of the operations of cluster controllers 244, frames beingconveyed to and from them are statistically multiplexed onto TDM bus140, thereby greatly increasing the traffic-carrying capacity of thebandwidth of TDM bus 140 over alternative transmission techniques.

An illustrative LAPD frame 300 is shown in FIG. 7. For purposes of thisdiscussion, it comprises a plurality of fields 301-305: a flag field301, used for delimiting frames; a Data Link Connection Identifier(DLCI) field 302; a control field 303 which specifies the type of LAPDframe this is; a user data field 304 which contains the level-3 protocol(packet) 350 or 351 referred to above; and a frame check sequence (FCS)field 305, used for error checking. The DLCI field 302 is the frameend-to-end address field. It contains a virtual link number or index(DLCI) that associates the frame with a particular call. In the forwarddirection, the DLCI identifies a particular channel element 245; in thereverse direction, the DLCI identifies a particular one of a plurality(illustratively two) of virtual ports of processor 602 which correspondto a particular speech processing unit 264 service circuit 612 (see FIG.6). Within a cluster controller 244, the DLCI identifies the channelelement 245 which is the source or destination of the frame. In thisembodiment, DLCIs are assigned to ports and channel elementsadministratively at system configuration time, and remain fixedthereafter.

The transmission of frames to and from cluster controllers 244 iseffected using the frame-relay technique of transmission, wherebyprotocol termination of the frames occurs only at the transmissionendpoints, thereby greatly increasing the efficiency and speed of thoseframe transfers through the system of FIG. 2. The frame-relay techniqueis described in U.S. Pat. No. 4,894,822. It is hereby incorporatedherein by reference.

Advantageously, in order to provide radio telephone services toconventional analog or digital TDMA mobile telephones 103 within thesame system, analog FM or TDMA digital radios 143 may also be connectedto TDM bus 140 in cells 202, in the manner described for cells 102, assuggested by the dashed blocks in FIG. 3. Alternatively, conventionalcells 102 may be used side-by-side with cells 202 within the system ofFIG. 2. TDMA traffic may be carried through the system of FIG. 2 eitherin circuit-switched form, like the analog radio traffic, or inpacket-switched form, like the CDMA traffic.

In the cell 202 of FIG. 3, DS1 interfaces 242 perform their conventionalfunctions of gathering 64 Kbps time slots from TDM bus 140 andmultiplexing them into DS1 format for transmission on trunks 207, andvice versa. It is important for purposes of this application that eachinterface 242 ensure that the delay undergone by signals of every DS0channel within interface 242 be constant; many commercial DS1interfaces, such as the AT&T TN 464C, do in fact meet this condition. Onaccount of the functions performed by cluster controllers 244, framesare statistically multiplexed onto trunks 207 and the format offacilities that implement trunks 207 is, from a logical perspective, nolonger the purely conventional DS1 format of facilities that implementtrunks 107 of FIG. 1: as opposed to comprising 24 independent DS0channels, as it does on DS1 facilities, each facility now comprisesmultiple independent "pipes" each consisting of the bandwidth of one ormore DS0 channels. Each of the "pipes" carries the LAPD frames createdby or destined for a single cluster controller 244. The traffic-carryingcapacity of the bandwidth provided by trunks 207 is thereby greatlyincreased over alternative transmission techniques, such as theconventional circuit-switching technique. Any remaining trunks 207(i.e., DS0 channels) that are not bundled into "pipes" continue to beused on an independent individual circuit-switched basis, e.g., to carrycommunications to and from conventional radios 143.

A cell interconnect module (CIM) 209 is shown in FIG. 4. Cellinterconnect module 209 is illustratively founded on the UniversalModule of the AT&T Definity communications system. It includes a localarea network (LAN) bus 250 operating under control of a controller 251.Universal DS1 (UDS1) interfaces 252 connect trunks 207 to LAN bus 250.Each interface 252 includes a DS1 trunk interface 442 which duplicatesthe DS1 facility-interface circuitry of DS1 interface 242, and a packetprocessing element (PPE) 401, interconnected by a concentration highway400. Concentration highway 400 is a time-division multiplexed bus of 64time slots each having a 64 Kbps rate. The DS1 trunk interface 442performs the functions of gathering 64 Kbps time slots fromconcentration highway 400, inverting the inverted HDLC format (discussedin conjunction with cell 202 of FIG. 3) back to normal, and multiplexingthe data into DS1 format for transmission on trunks 207, and vice versa.

PPE 401 performs LAPD frame-relay functions between concentrationhighway 400 and LAN bus 250. PPE 401 includes a translation table 411that contains a board and a port address for each DLCI 302. Translationtable 411 is administered at initialization. PPE 401 is administered toreceive LAPD frames 300 on designated time slots of concentrationhighway 400. For each LAPD frame 300 received on concentration highway400, PPE 401 uses the contents of the frame's DLCI field 302 to find thecorresponding board and port address in table 411. The board and portaddresses identify the intended recipient of frame 300 on LAN bus 250.PPE 401 then strips flag field 301 from frame 300 and prepends the foundboard and port addresses to the frame to form a modified LAPD frame 310shown in FIG. 8. A comparison with FIG. 7 shows flag field 301 to havebeen replaced by board address 311 and port address 312. PPE 401 thentransmits modified LAPD frame 310 on LAN bus 250. In the otherdirection, PPE 401 examines modified LAPD frames 310 transmitted on LANbus 250 for its board address 311. It receives any frame 310 having thelooked-for address 311, strips the addresses 311 and 312 from frame 310,replaces them with flag field 301 to form a LAPD frame 300, and thentransmits frame 300 on concentration highway 400. The stripped-off portaddress 312 identifies to PPE 401 the particular time slots on whichthat particular frame 300 is to be transmitted.

Also connected to LAN bus 250 of cell interconnect module 209 areexpansion interfaces (EIs) 253. Each expansion interface 253 couples anoptical fiber trunk 210 to LAN bus 250. Expansion interfaces 253 merelyact as routing elements. Each expansion interface 253 includes a LAN businterface 450 which monitors LAN bus for modified LAPD frames 310 havinga pre-administered DLCI 302, board address 311, and port address 312.Interface 450 captures any frame 310 having the looked-for DLCI 302,board address 311, and port address 312, strips off the prepended boardaddress 311, and stores the frame 310 in a FIFO buffer 451. FIFO buffer451 outputs the prepended port address 312 and DLCI 302 of the frame 310to a translation table 452, and outputs fields 302-305 of frame 310 to atranslation inserter 453. Table 452 is a pre-administered table of boardand port addresses of speech coder modules 220. Table 452 uses the portaddress 312 and DLCI 302 that it receives from FIFO buffer 451 as apointer to find a new board address 311 and port address 312 for theframe 310, and sends the new addresses 311 and 312 to translationinserter 453. Inserter 453 prepends the new board and port addresses 311and 312 received from table 452 to the frame 310 fields that it receivedfrom FIFO buffer 451, and sends the new frame 310 to fiber interface454. If no corresponding addresses are found in and sent from table 452,inserter 453 merely discards the received frame 310. Fiber interface 454transmits the frame 310 on optical fiber trunk 210. Any desired protocoland transmission format may be used on trunks 210. In the reversedirection, fiber interface 454 receives frames 310 on trunk 210 andstores them in a FIFO buffer 455. LAN bus interface 450 extracts thestored frames 310 from FIFO buffer 455 and transmits them on LAN bus250. Consequently, expansion interface 253 merely transmits on LAN bus250 those frames 310 that it receives on the attached fiber trunk 210.These frames 310 have board addresses 311 that identify the destinationinterfaces 252 on LAN bus 250, and port addresses 312 that are notlooked for by any expansion interfaces 253 on LAN bus 250.

For purposes of handling conventional, circuit-switched, cellular radiotelephone communications, cell interconnect module 209 includes elementsshown in dashed lines in FIG. 4. Specifically, CIM 209 includes a TDMbus 230 which duplicates TDM bus 130, and each UDS1 interface 252includes a time-slot interchanger (TSI) 402 which couples concentrationhighway 400 to TDM bus 230. TSI 402 performs conventional time-slotinterchange functions. It receives designated 64 Kbps channels (timeslots) on concentration highway 400 and TDM bus 230 and transmits themon designated time slots of TDM bus 230 and concentration highway 400,respectively. TSI 402 is programmed on a per-call basis. For the purposeof switching these conventional communications, TDM bus 230 is coupledby a TMS interface 133 and trunk 109 to a TMS 121 (see FIG. 2), in themanner described for FIG. 1. For the purpose of connecting theseconventional communications to public telephone network 100, TDM bus 230is also coupled by a DS1 interface 132 and a trunk 106 to network 100.

A speech coder module 220 of a digital cellular switch 201 is shown inFIG. 5. Each DCS 201 comprises one or more identical modules 220. Module220 is illustratively the Universal Module of AT&T Definitycommunications system. Module 220 includes TDM bus 130 and a LAN bus 260which is a duplicate of LAN bus 250, both operating under control of acontroller 231. As in FIG. 1, TDM bus 130 is connected by DS1 interfaces132 and trunks 106 to public telephone network 100. Fiber trunks 210from cell interconnect modules 209 are connected to LAN bus 260 byexpansion interfaces 263 which duplicate expansion interfaces 253. Eachcell interface module 209 of a DCS 201 is connected to each speech codermodule 220 of that DCS 201. Interconnection between DCSs 201 is providedby network 100 through trunks 106.

Buses 260 and 130 are interconnected through a plurality ofcall-processing nodes referred to herein as speech processing units(SPUs) 264. Based on the board address 311 prepended to each frame 310by expansion interfaces 253 of cell interconnect modules 209, eachspeech processing unit 264 receives frames 310 that are addressed to it,depacketizes their contents (i.e., terminates their protocol), performsvarious processing functions--including speech decompression--on thecontents of each received frame, and outputs the processed framecontents on TDM bus 130 in time slots which are assigned to calls on acall-by-call basis. In the reverse direction, a speech processing unit264 receives communications over TDM bus 130 in time slots which areassigned to calls on a call-by-call basis, performs various processingfunctions--including speech compression--thereon, packetizes theprocessed communications, includes in each frame a DLCI 302 identifyinga particular channel element 245 of a particular cell 202, prepends toeach frame board and port addresses 311 and 312 that identify theframe's destination on LAN bus 260, and transmits the frames 310 on LANbus 260.

As a consequence of the operations of cell interconnect modules 209 andspeech coder modules 220, frames 310 being conveyed between them arestatistically multiplexed onto, and frame-relayed over, trunks 210,thereby greatly increasing the traffic-carrying capacity of thebandwidth provided by trunks 210 over alternative transmissiontechniques such as circuit-switching.

As was mentioned in conjunction with FIG. 3, DCS 201 optionally includesa TMS 121 for servicing conventional radio telephone communications.Speech coder module 220 is connected to TMS 121 by a trunk 109 and a TMSinterface 133, in the manner described for switching modules 120 of FIG.1.

An illustrative speech processing unit 264 is shown in FIG. 6. Each SPU264 includes a LAN bus interface 601. It monitors frames 310 traversingLAN bus 260 for pre-administered board addresses 311, and captures thosehaving the sought-for addresses 311. LAN bus interface 601 includes abuffer 620. Upon capturing a frame 310, LAN bus interface 601 appends toit a time stamp, stores it in the buffer 620, and issues an interrupt toa processor 602. The time stamp is the present count of counter 623,discussed further below.

The port address 312 of a frame 310 identifies one of a plurality ofservice circuits 612 implemented by SPU 264. A service circuit 612 isassigned to a call either for the duration of the call or until a hardhandoff occurs. Each service circuit 612 has its own audio-processingcircuitry. But all service circuits 612 are served on a time-sharedbasis by processor 602, which performs frame-selection andprotocol-processing functions for all service circuits 612 of an SPU264. The functions performed by processor 602 on frames 310 receivedfrom LAN bus interface 601 are shown in FIGS. 11-14, and 17-18, andfunctions performed by processor 602 on traffic segments (hereinafteralso referred to as traffic frames) received from service circuits 612are shown in FIG. 15. Processor 602 performs each of these functions foreach service circuit 612 every 20 msecs. The performance of thefunctions is interrupt-driven, by interrupt signals provided by anadaptive synchronization circuit 611 and interface 601.

The exchange of traffic frames of incoming and outgoing call traffic iscarried on between processor 602 and service circuits 612 throughbuffers 603 of processor 602. Each service circuit 612 has its owncorresponding buffer 603. A buffer 603 buffers traffic frames passingbetween processor 602 and a vocoder 604 of a service circuit 612 tocompensate for minor differences and fluctuations in the timing of inputand output operations of processor 602 and vocoder 604.

Each service circuit 612 has its own vocoder 604. Vocoders 604 providevoice compression and decompression functions. Each is a digital signalprocessor that receives a traffic frame of compressed speech fromprocessor 602 via buffer 603 at regular intervals (e.g., every 20msecs.) and decompresses the traffic frame into a predetermined number(e.g., 160 bytes) of pulse-code-modulated (PCM) speech samples. Eachbyte has a duration of 125 usecs. in this example, referred to as a"tick". In the opposite direction, a vocoder 604 receives 160 bytes ofPCM speech samples, performs speech compression functions thereon, andoutputs a traffic frame of the compressed speech to processor 602 viabuffer 603 at regular intervals (every 20 msecs.). Exchanges of trafficframes between vocoder 604 and processor 602 are timed by clock signalsgenerated by vocoder 604 internal input and output clocks 621 and 622,while receipt and transmission of PCM samples by vocoder 604 are timedby clock signals generated by a clock circuit 600. Clocks 621 and 622are edge-synchronized with circuit 600 clock signals at systeminitialization and service circuit 612 reset. Vocoders are well known inthe art. Each vocoder 604 is illustratively implemented using the AT&T16A digital signal processor (DSP) which embodies the Qualcomm, Inc.QCELP low-bit-rate variable-rate speech encoding/decoding algorithm. TheQCELP algorithm provides for sending minimal information during periodsof low or no speech activity. The frame transport mechanism of thisembodiment ideally adapts to time-varying traffic loads.

In the case of a system handling both CDMA and TDMA traffic wherein theTDMA traffic is also frame-relayed, some of the service circuits 612 arededicated to handling the TDMA traffic, and their vocoders 604 areillustratively the AT&T 16A digital signal processor programmedaccording to the TIA IS-54 standard for TDMA communications.

PCM samples on their way from vocoders 604 pass through tone-insertioncircuits 605. Each service circuit 612 has its own tone-insertioncircuit 605. Upon command from processor 602, a tone-insertion circuit605 momentarily blocks and discards PCM samples output by vocoder 604,and in their place substitutes PCM samples of whatever Touch-Tonesignals were specified by the command. Tone-insertion circuit 605 has noeffect on PCM samples being input to vocoder 604. Operation oftone-insertion circuit 605 is synchronized with the output of vocoder604 by clock signals generated by clock circuit 600.

Tone-insertion circuits 605 are followed in the sequence of servicecircuit 612 circuitry by echo cancellers 606. Each service circuit 612has its own echo canceller 606. Each cancels echoes of telephone network100-bound call traffic from telephone network 100-originated calltraffic, by keeping an attenuated copy of the vocoder-generatednetwork-bound traffic and subtracting an appropriately-delayed copy fromreceived network-bound traffic. Echo cancellers are well known in theart. Timing of echo canceller 606 operations is controlled by clocksignals generated by clock circuit 600.

Echo cancellers 606 receive network-originated traffic from, andtransmit network-bound traffic to, a concentration highway 607.Concentration highway 607 is a passive serial TDM bus that carries 64kbps time slots. Each echo canceller 606 is statically assigned its owninput time slot and its own output time slot on concentration highway607.

Concentration highway 607 is coupled to TDM bus 130 by a TDM businterface 608. Interface 608 performs time-slot interchange (TSI)functions between highway 607 and bus 130. Its operation is timed byclock signals generated by circuit 600, and is controlled by atranslation and maintenance (XLATION. AND MTCE.) unit 609. Unit 609performs highway 607-to-bus 130 time-slot assignment functions on aper-call basis, under the direction of controller 231 of that speechcoder module 220. Unit 609 communicates with controller 231 via acontrol channel implemented by bus 130. This control channel isinterfaced to unit 609 through interface 608 and bus 613. Unit 609provides maintenance functions to LAN bus interface 601 via control link616.

Unit 609 exerts control over interface 608 via a translation andmaintenance control bus 613, to which both are connected. Similarly,processor 602 controls circuits 601, 603-606, and 611 via a processorcontrol bus 610. Communications between processor 602 and unit 609 arefacilitated by a buffer 614 which couples bus 610 with bus 613.

Clock circuit 600 is connected to TDM bus 130 and derives timinginformation therefrom, in a conventional manner. Clock circuit 600distributes this information, in the form of clock signals of variousrates, including 2.048 MHz, 8 KHz, and 50 Hz (corresponding to intervalsof 500 nsec., 125 usec., and 20 msec. intervals, respectively), all ofwhich are synchronized with each other, via a clock bus 615 to circuits604-606, 608, and 611, in order to synchronize their operation with TDMbus 130. Clock circuit 600 also distributes this information to LAN businterface 601 for bit-time synchronization of LAN bus 260. Operation ofTDM bus 130 is synchronized to network 100--hence, clock circuit 600synchronizes operations of the various elements with the master clock ofnetwork 100.

Adaptive synchronization circuit 611 uses the clock signals obtainedfrom clock circuit 600 to generate clock signals which are synchronizedin frequency with, but are offset in phase--in amounts controlled byprocessor 602--from, the 20 msec. clock signals generated by clockcircuit 600. These offset clock signals are used to time the operationsof processor 602. The generation and use of these offset clock signalsis explained further below. Physically, circuits 611 and 600 may beimplemented as a single device.

Circuit 611 also includes a present-time counter 623. Counter 623increments its count once every PCM sample tick, e.g., once very 125usecs. This count is reset by every 50 Hz clock pulse from clock circuit600, e.g., every 20 msecs. Counter 623 thus indicates present timerelative to signals generated by clock circuit 600. A second portion ofcounter 623 keeps a modulo-8 count that is incremented by the 20 msec.clock pulses that reset the 125 usec. count. Counter 623 provides itscounts to LAN bus interface 601 for use as a time stamp of receivedframes 310.

Discussion now returns to processor 602 and its packet-andframeprocessing functions. (Level-2 protocol processing is commonlyreferred to as frame processing, while level-3 protocol processing iscommonly referred to as packet processing.) The functions performed byprocessor 602 on frames 310 received from LAN bus 260 are shown in FIGS.11-14. Processor 602 performs these functions for each service circuitevery 20 msecs. Performance of different ones of these functions for aparticular service circuit 612 is triggered by receipt of correspondingreceive interrupt signals from LAN bus interface 601 and adaptivesynchronization circuit 611.

As was mentioned above, upon receiving a frame addressed to thecorresponding SPU 264, LAN bus interface 601 appends a time stamp to thereceived frame, stores the received frame in buffer 620, and issues aninterrupt to processor 602. Upon being invoked by the receive interruptsignal from LAN bus interface 601, at step 900, processor 602 retrievesthe received frame from buffer 620 of LAN bus interface 601, at step902. Processor 604 then performs conventional level-2, i.e., LAPDprotocol, processing on the frame, at step 904. This processing mayinclude acknowledging receipt of the frame. Upon completing level-2processing, processor 604 checks control field 303 to see if this is alevel-2 only frame (e.g., a loop-around test frame), at step 906. If so,processing of the frame is completed, and processor 602 merely returnsto the point of its invocation, at step 908. But if this is not alevel-2 only frame, i.e., its user data field 304 carries a level-3protocol, processor 602 uses the frame's DLCI 302 to select from itsmemory the stored call state of the call to which the frame pertains, atstep 910. Next, processor 602 checks, at step 911, packet type field 321of the received level-3 protocol to determine the packet type: trafficor signalling. If field 321 identifies the packet as a signallingpacket, it means that the packet carries cell-to-switch signallinginformation, i.e., signalling intended for DCS 201. Processor 602therefore performs the signalled function, at step 970. This may be anyone of 3 functions: to update call state by either setting up or tearingdown a call or adding or removing a second cell in soft handoff, toinsert tones into the telephone networkbound portion of the call, or toperform initial clock synchronization (discussed in conjunction withFIG. 17). Processor 602 then returns to the point of its invocation, atstep 946. Voice/signalling packets 350 are sent and received at 20 msec.intervals, while signalling-only packets 351 may be sent at any time asrequired to send signalling information.

If field 321 identifies the packet as a traffic packet, processor 602performs clock adjustment and synchronization functions, at step 912, toshift the offset of clock signals generated by circuit 611 from clocksignals generated by circuit 600 by an amount determined by processor602 or dictated by clock adjust field 322 of the received packet. Theseare described in conjunction with FIG. 18. Processor 602 then checksvoice/signalling type field 326 of the received level-3 packet, at step914, to identify the type of information carried by the packet: voiceonly, voice plus signalling, or signalling only. If the traffic packetis a voice-only packet, processor 602 checks the retrieved call state todetermine if the call is in soft handoff, at step 916. If not, processor602 checks air CRC field 323 of the frame (containing the result of acheck-sum computed over the CDMA transmission between cell 202 andmobile telephone 203), at step 918. If the air CRC does not check out,it means that the packet carries defective information, and so processor602 discards the packet, at step 923, and then returns, at step 946.Vocoder 604 will mask the loss of that traffic. If the air CRC checksout at step 918, processor 602 checks signal quality field 324 of thepacket to determine whether the voice quality meets a predeterminedthreshold value, at step 919. If the voice quality does meet thethreshold value, processor 602 marks the packet as "good" by appending acommand thereto, at step 920, stores the packet of voice information inbuffer 603 which is allocated to the appropriate service circuit 612, atstep 922, and then returns to the point of its invocation, at step 926.If the voice quality does not meet the minimum threshold value,processor 602 marks the packet as "bad", at step 921, stores the packetin buffer 603 of the appropriate service circuit 612, at step 922, andthen returns, at step 946.

During the procedures just described, processor 602 uses contents ofsequence number field 320 of the received packet to detect and handlelost or out-of-sequence packets, in a conventional manner.

Returning to step 916, if the call is in "soft handoff", processor 602should be receiving two packets for the call every 20 msecs., each froma different cell 202 but generally carrying identical information. Soprocessor 602 checks whether it has yet received both duplicate packets,at step 932. The duplicate packets are identified by having the samesequence number in field 320. If not, meaning that processor 602 hasreceived either only one of the expected duplicate packets, or hasreceived packets from both cells but bearing different sequence numbers,processor 602 checks the sequence number of the just-received packet, atstep 933, to determine whether its sequence number is greater than,equal to, or less than the expected sequence number. If the sequencenumber of the received packet is greater than the expected sequencenumber, processor 602 stores the received packet, at step 934, updatesthe associated call's state to indicate that one of the packets thatwill be expected in the future has been received, at step 935, andreturns, at step 946. Updating of the call state at step 935 includesstoring the contents of power control field 325 of the received packet.If the sequence number of the received packet is equal to the expectedsequence number, processor 602 proceeds to steps 918 et seq. to processthe packet as described previously. And if the sequence number of thereceived packet is less than the expected sequence number, processor 602discards the received packet, at step 936, and then returns, at step946. Again, vocoder 604 will mask the loss of that traffic.

Returning to step 932, if processor 602 finds that it has received bothexpected packets, processor 602 updates the call state to so indicate,at step 938. This includes storing the contents of power control field325 of the received packet. It then retrieves the first-receivedexpected packet (now stored in a buffer 603) and compares the air CRCand the signal quality indicia of both packets to determine which packetis better, at step 940. Processor 602 then checks the voice qualityfield of the better packet to determine whether the voice quality meetsa predetermined threshold value, at step 941. If not, processor 602marks the better packet as "good" by appending a command thereto, atstep 943; if so, processor 602 marks the better packet as "bad", at step942. Processor 602 then discards the worse packet and stores the betterpacket in buffer 603 of the corresponding call channel, at step 944.Processor 602 then returns, at step 946.

Turning to FIG. 12, following step 946, when processor 602 is invoked atstep 950 by a receive interrupt signal RX₋₋ INT₋₋ X for a particular(Xth) service circuit 612, processor 602 checks buffer 603 correspondingto that service circuit 612 to determine if buffer 603 is empty, at step951. If not, processor 602 retrieves the contents of that buffer 603 andpasses the retrieved contents to vocoder 604 of that service circuit612, at step 952. If buffer 603 is empty, processor 602 invokes afunction in vocoder 604 of the appropriate service circuit 612 to maskthe loss of the voice segment carried by the discarded packet, at step953. Vocoder 604 masks the loss by generating at its output to circuit605 PCM samples that it generates as a function of previously-receivedpackets. Processor 602 then returns to the point of its invocation, atstep 954.

Returning to step 914, a traffic packet that carries signallinginformation is encountered by processor 602 only during "soft handoff",as under normal circumstances signalling is sent directly to mobiletelephone 203 from cell 202 involved in a given call. If the trafficpacket carries only signalling information, processor 602 proceeds tostep 955 of FIG. 13. There, processor 602 checks further contents ofvoice/signalling type field 326, to determine the signalling direction:forward and/or reverse. If the direction is forward, identifying thesignalling as being originated by a cell 202 and destined for a mobiletelephone 203, processor 602 merely stores the packet, at step 956, andthen returns, at step 970. If both signalling directions are indicated,processor 602 stores the forward signalling, at step 957, and thenproceeds to step 958. If the direction is reverse, identifying thesignalling as being originated by a mobile telephone 203 and destinedfor cells 202, processor 602 checks, at step 958, whether it hasreceived signalling packets from both sides (i.e., from both of thecells 202 involved in the "soft handoff"). If not, processor 602 storesthe packet, at step 960, and then updates the corresponding call's stateto indicate that a signalling packet from one side has been received, atstep 962. Processor 602 then returns, at step 970. If the check at step958 reveals that signalling packets from both sides have been received,processor 602 updates the corresponding call's state to so indicate, atstep 964, and then compares the air CRC and signal quality fields 323and 324 of the two packets to determine which packet carries the betterquality signals, at step 966. Processor 602 then discards the worsepacket and stores the better one, at step 968, and then returns, at step970.

Returning to step 914, if processor 602 determines that the packetcarries both voice and signalling information, processor 602 proceeds tostep 985 of FIG. 14, and performs signalling-processing steps 985-998 ofFIG. 14 which duplicate steps 955-968 of FIG. 13, and then proceeds tostep 932 of FIG. 11 to perform the voice-processing steps.

The functions performed by processor 602 on traffic frames (segments ofvoice information) received from vocoders 604 are shown in FIG. 15.Processor 602 performs these functions for each service circuit 612every 20 msecs. The performance of the functions for a particularservice circuit 612 is also interrupt-driven, by receipt of acorresponding transmit interrupt signal provided by adaptivesynchronization circuit 611.

Upon being invoked by a transmit interrupt signal TX₋₋ INT₋₋ X to startprocessing for a particular (Xth) service circuit 612, at step 1200,processor 602 checks the stored call state of the call that is beingserved by this service circuit 612 to determine whether the call is insoft handoff, at step 1202. If not, processor 602 accesses vocoder 604of the service circuit 612 that is being served and requests therefrom atraffic frame of full-rate-coded call information, at step 1227. Uponreceiving a traffic frame from that vocoder 604, at step 1228, processor602 formats the traffic frame in the level-3 protocol, at step 1230.This includes prepending a sequence number and a traffic type to thecall traffic. Processor 602 then conventionally encapsulates theformatted traffic frame in LAPD frame format, at step 1232, to form aframe 300 (see FIG. 7). This includes retrieving the DLCI which isassociated with the mobile-bound direction of the call and whichidentifies a particular channel element 245 of a particular cell 202(see FIG. 3) that is serving the call, and including it in LAPD frame300. Processor 602 then uses this DLCI to find in a table the board andport addresses 311 and 312 that correspond to this DLCI, and prependsthe found addresses 311 and 312 to LAPD frame 300 to form a modifiedLAPD frame 310 (see FIG. 8), at step 1234. Processor 602 hands frame 310over to LAN bus interface 601 for transmission onto LAN bus 260, at step1236. Processor 602 then returns to the point of its invocation, at step1238.

Returning to step 1202, if processor 602 determines that the call is insoft handoff, it checks the stored call state of the call to determinewhether any forward signalling is stored for this circuit, at step 1204.Forward signalling would have been received only from the cell 202 thathas been handling the call (referred to as the master cell 202) andstored at step 956 or 957 of FIG. 13, or step 986 or 987 of FIG. 14. Ifforward signalling is not stored, processor 602 accesses vocoder 604 ofthe service 612 circuit that is being served and requests therefrom atraffic frame of full-rate-coded communication information, at step1206. But if forward signalling is stored, processor 602 must reserveroom in a packet for the forward signalling information, and so itaccesses vocoder 604 and requests therefrom a traffic frame of onlypartial-rate-coded communication information, at step 1208.

Vocoder 604 typically supplies traffic frames of full-rate-codedinformation, and it may not be able to respond to the request for atraffic frame of partial-rate-coded information instantly. Further,given a pause in speech activity, a partial-rate coded traffic frame maybe supplied even if a full-rate-coded traffic frame has been requested.Processor 602 will check for this condition, at step 1218.

When it has received a traffic frame from vocoder 604, at step 1209,processor 602 duplicates the traffic frame, at step 1210, so as to haveduplicate copies to send to both cells 202 that are involved in the softhandoff. At step 1212, processor 602 then retrieves power controlinformation that will have been stored at steps 935 and 938 of FIG. 11from both cells 202 that are involved in the soft handoff, swaps it sothat each of the two cells 202 will be sent the power controlinformation that was received from the other of the two cells 202, andinserts the swapped information into the duplicate packets as powercontrol field 325, at step 1212. Processor 602 then checks the call'sstate to determine whether reverse signalling for the call has beenreceived and stored at step 968 of FIG. 13 or step 998 of FIG. 14, atstep 1214. If reverse signalling is available, processor 602 appends itto both of the duplicate packets, at step 1216. Following step 1216, orif no reverse signalling is available, processor 602 checks whether ithad been supplied by vocoder 604 with a frame of full-rate-coded orpartial-rate-coded information, at step 1218. If the traffic frame isfull-rate-coded, it has no room for forward signalling information, andso processor 602 proceeds to steps 1230 et seq. to format, packetize,and transmit both of the duplicate packets. Packetization at step 1234involves including in each duplicate packet's frame protocol 300 adifferent DLCI, so that the two packets will each travel to a differentcell 202 involved in the soft handoff. Returning to step 1218, if thetraffic frame is partial-rate-coded, processor 602 checks the call'sstate to determine whether forward signalling for the call had beenreceived and stored at step 956 of FIG. 13 or step 986 of FIG. 14, atstep 1220. If forward signalling is available, processor 602 appends itto both of the duplicate packets, at step 1222. Following step 1222, orif no forward signalling is available, processor 602 proceeds to steps1230 et seq.

The synchronization of cell 202 and SPU 264 operations will now beexplained in greater detail in conjunction with FIGS. 16-22.

FIG. 19 represents the scenario for initial timing adjustments fortraffic flow from network 100 to mobile radio-telephones 203. As wasmentioned above, the operations of all mobile radio-telephones 203 andall channel elements 245 of all cells 202 are driven and synchronized toa common timing signal, which may be a signal broadcast by a globalpositioning satellite. Each cell 202 derives therefrom a 20 msec. cellclock 1000 signal, which triggers each channel element 245 involved in acall to make a transmission to the corresponding mobile telephone 203every 20 msecs. at time 1300. A programmed, constant, offset (which maybe zero) may exist for a given call (i.e., an offset between the risingedge of cell clock 1000 and time Tx 1300). This constant offset affectsthe relative positions of signals 1304, 1307, 1308, and 1309 by theamount of said offset.

In order to be able to transmit call traffic at time 1300, a channelelement 245 must receive that call traffic at least some minimum periodof time prior to time 1300, at a time t_(min) 1301. Channel element 245preferably receives the information for transmission within a timewindow 1302, which exists a little after time 1300 of the priortransmission and a little before time 1301 of the present transmission.Window 1302 thus provides some leeway for minor time fluctuations.However, when a call is being established, it is uncertain when channelelement 245 that is handling the call will receive a packet of calltraffic for transmission from SPU 264. This is because, as was mentionedpreviously, the operations of mobile telephone switches 201 arecontrolled by a different clock than that of cells 202, which clock isnot synchronized with, but is independent of, cell clock 1000.Furthermore, other factors, such as differences in distances betweenmobile telephone switches 201 and different cells 202 and differenttraffic loads being conveyed between them--and consequent differenttransmission delays between them--also make the time of receiptuncertain. Therefore, when a call path is first established between achannel element 245 and an SPU 264 and null traffic begins to flowbetween them, packets from SPU 264 may be received by channel element245 at times 1303 that are outside of windows 1302 and--in the worstcase--are after times t_(min) 1301. If that is the case, the channelelement's corresponding channel controller 244 sends a signalling packetto SPU 264 indicating a need to adjust the time of transmission ofpackets from SPU 264 and also indicating the amount of time by whichthat transmission time must be adjusted to position the time of receiptof the packets at channel element 245 safely within windows 1302.

The clock adjustment functions performed at cell 202 are shown in FIG.16. They constitute a processor-performed routine invoked upon receiptof a packet at cluster controller 244. When the routine is invoked, atstep 1001, it checks whether the received packet is the first trafficpacket received for the call, at step 1002. If so, the routine comparesthe time at which the packet was received with a window 1302 (thedefinition of which is stored in cluster controller 244), at step 1004,to determine, at step 1006, when in relation to window 1302 the packetwas received. If the packet was received substantially in the center ofwindow 1302, no clock adjustment is necessary and the routine merelyreturns to the point of its invocation, at step 1022. If the packet wasreceived too early, the routine causes a cell-to-switch type ofsignalling packet to be sent to processor 602 of SPU 264 that ishandling the call, at step 1008, requesting processor 602 to delay thetime of the TX₋₋ INT₋₋ X interrupts for this call by a time, alsospecified in the packet, such as will move the time of receiptsubstantially to the center of window 1302. Conversely, if the packetwas received too late, the routine causes a cell-to-switch type ofsignalling packet to be sent to processor 602, at step 1010, requestingthat the time of the TX₋₋ INT₋₋ X interrupts for this call be advancedby a specified time. The routine then returns to the point of itsinvocation, at step 1022.

Alternatively, the routine need not respond merely to the first trafficpacket received, but may calculate an average time of required clockadjustment based on the receipt of a plurality of received trafficpackets.

Packet receive times 1303 at channel element 245 correspond to packettransmit times 1304 at SPU 264. As was mentioned previously,transmission of packets to channel element 245 from SPU 264 is triggeredby transmit interrupt signals TX₋₋ INT₋₋ X issued to processor 602 byadaptive synchronization circuit 611. Consequently, adjustment of thepacket receive times at channel element 245 by a certain amount requiresan adjustment of TX₋₋ INT₋₋ X signals at circuit 611 by the same amount.Therefore, when processor 602 receives the abovementioned signallingpacket from channel element 245, it responds thereto at step 970 of FIG.11 by commanding adaptive synchronization circuit 611 to adjust the TX₋₋INT signal for the corresponding service circuit 612 by the specifiedamount. Circuit 611 obliges and shifts that transmit interrupt signal bythe specified time period, designated as 1310 in FIG. 19. Packettransmission time is thus shifted from times 1304 to times 1305 at SPU264, which corresponds to packet receive times 1306 at channel element245. Packet receive times 1306 lie within windows 1302.

However, in order to be able to transmit a packet at a given time,processor 602 must receive the traffic frame (segment of call traffic)which is included in that packet from vocoder 604 at some time prior tothe transmit time. Packet transmit times 1304 correspond to framereceipt times 1307, which in turn correspond to vocoder 604 trafficframe transmit times 1308, whereas shifted packet transmit times 1305correspond to shifted traffic frame receipt times 1311, which in turncorrespond to vocoder 604 traffic frame transmit times 1309.Consequently, processor 602 must cause vocoder 604 to shift its trafficframe transmit times from times 1308 to times 1309.

Vocoder 604 uses the output of an internal output clock 622 to time itstraffic frame transmissions. Clock 622 of an Xth service circuit 612 isinitially synchronized to clock input signals received from clockcircuit 600. Processor 602 sends a command to vocoder 604 to adjust theoffset of its output clock 622 signals from the circuit 600 clock inputsignals by the abovementioned time period 1310 that was specified in thesignalling packet which processor 602 received from channel element 245.Vocoder 604 does so, thereby shifting its traffic frame transmit timesfrom times 1308 to times 1309. The net result is that the asynchronousoperations of channel element 245 and service circuit 612 and processor602 have been synchronized with each other.

The response scenario of processor 602 to receipt of the clock-adjustsignalling packet from cell 202 is charted in FIG. 17. Upon determiningthat the received signalling packet requests clock adjustment to beperformed, at step 1050, processor 602 checks contents of the packet todetermine the direction in which the timing signals are to be moved, atstep 1052. If they are to be delayed, processor 602 sends a command toadaptive synchronization circuit 611 to retard subsequent TX₋₋ INT₋₋ Xinterrupt signals by the amount of time specified in the packet, at step1054. Processor 602 also sends a command to vocoder 604 to increase theoffset of its output clock 622 form clock 600 signals by the same amountof specified time, at step 1056, and then returns, at step 1062. If thetiming signals are to be moved forward in time, processor 602 sends acommand to adaptive synchronization circuit 611 to advance subsequentTX₋₋ INT₋₋ X interrupt signals by the amount of time specified in thereceived signalling packet, at step 1058. Processor 602 also sends acommand to vocoder 604 to decrease the offset of its output clock 622from clock 600 signals by the same amount of specified time, at step1060, and then returns, at step 1062.

FIG. 20 represents the scenario for initial timing adjustments fortraffic flow from mobile radio-telephones 203 to network 100. As wasmentioned above, mobile radio-telephones 203 and cells 202 aresynchronized with each other. A clock corresponding to cell clock 1000(derived by mobile telephone 203 from traffic received by it from cell202) causes a mobile radio-telephone 203 to make a transmission every 20msecs. to channel element 245 that is handling the call, causing channelelement 245 to receive those transmissions at times 1400 and to conveythem in packets to SPU 264 at times 1403. Packet transmit times 1403 atchannel element 245 correspond to packet receive times 1404 at processor602 of SPU 264. Receive times 1400 are relatively offset from cell clock1000 by the amount of a programmed, constant, offset at cell 202 withrespect to transmit times 1300. Thus, an offset in transmit times 1300results in a like offset in receive times 1400. This offset iscompensated for by the mechanisms described herein.

Reception of packets from channel element 245 for a particular (Xth)service channel 612 is triggered at processor 602 by a receive interruptsignal RX₋₋ INT₋₋ X for that service channel 612, generated by adaptivesynchronization circuit 611. Reception of the packets must precede bysome minimum time the transmission of the call traffic frames containedin the packets to vocoder 604, to give processor 602 sufficient time forprocessing of the packets. Initially, vocoder 604 expects to receivetraffic frames at times 1408, which correspond to traffic frametransmission times 1406 from processor 602. Consequently, in order to beable to transmit traffic frames to vocoder 604 at times 1406, processor602 must receive corresponding packets from channel element 245 no laterthan at times t_(min) 1401. Processor 602 preferably receives eachpacket within a time window 1402, which exists a little after transmittime 1406 of the prior frame transmission to vocoder 604 and a littlebefore time t_(min) 1401 of the present frame transmission. Window 1402thus provides some leeway for minor time fluctuations.

However when a call is being established, it is uncertain when processor602 will receive a packet of information from channel element 245, forthe same reasons as it is uncertain when channel element 245 willreceive a packet from processor 602, discussed above. Therefore, when acall path is first established between a channel element 245 and an SPU264 and null traffic begins to flow between them, packets from channelelement 245 may be received by processor 602 at times 1404 that areoutside of windows 1402 and--in the worst case--are after times t_(min)1401. Processor 602 cannot change the times 1403 at which channelelement 245 transmits packets, and therefore it cannot change the times1401 at which it receives those packets; processor 602 can only changethe times 1406 when it transmits frames to vocoder 604. Hence, if times1404 lie outside of windows 1402, processor 602 determines a time period1410 by which it needs to adjust its time of transmission of frames tovocoder 604 in order to position the times 1404 of its receipt ofpackets safely within windows 1402. Processor 602 then commands adaptivesynchronization circuit 611 to adjust the receive interrupt signal RX₋₋INT₋₋ X for the corresponding service circuit 612 by the specifiedamount. Circuit 611 obliges and shifts that receive interrupt signal bythe specified time period 1410. Frame transmission times from processor602 is vocoder 604 are thus shifted from times 1406 to times 1407, whichshifts packet receive times 1404 at processor 602 inside windows 1402.

However, in order to be able to shift its frame transmit times fromtimes 1406 to times 1407, processor 602 must cause vocoder 604 to shiftits frame receive times from times 1408 to times 1409. Vocoder 604 usesthe output of an internal input clock 621 to time its frame receptions.Like output clock 622, input clock 621 is synchronized to clock 600input signals. Processor 602 therefore sends a command to vocoder 604 toadjust the offset of its input clock 621 signals from the clock 600input signals by the abovementioned time period 1410. Vocoder 604 doesso, thereby shifting its frame receive times from times 1408 to times1409. Again, the net result is that the asynchronous operations ofchannel element 245 and service circuit 612 and processor 602 have beensynchronized with each other.

The just-described clock adjustment functions are performed by processor602 at step 912 of FIG. 11, and are shown in FIG. 18. Upon commencing toperform the clock adjustment function, at step 1070, processor 602determines from the retrieved call state and the received packet typewhether the received packet is the first traffic packet for the call, atstep 1072. If so, processor 602 compares the packet's receive time stamp(appended to the packet by LAN interface 601) with a window 1402 (thedefinition of which is computed and stored by processor 602 for eachcall that it is handling), at step 1073, to determine, at step 1074,when in relation to window 1402 the packet was received. If the packetwas received substantially in the center of window 1302, no clockadjustment is necessary, and processor 602 proceeds to step 1090. If thepacket was received too early, processor 602 commands adaptivesynchronization circuit 611 to advance subsequent RX₋₋ INT₋₋ X interruptsignals by the amount of time determined by processor 602 to benecessary to move the time of receipt substantially to the center ofwindow 1402, at step 1075. Processor 602 also sends a command to vocoder604 to increase the offset of its input clock 621 from clock 600 signalsby the same amount of specified time, at step 1076. Conversely, if thepacket was received too late, processor 602 commands adaptivesynchronization circuit 611 to retard subsequent RX₋₋ INT₋₋ X interruptsignals by the amount of time determined by processor 602 to benecessary to move the time of receipt substantially to the center ofwindow 1402, at step 1077. Processor 602 also sends a command to vocoder604 to decrease the offset of its input clock 621 from clock 600 signalsby the same amount of specified time, at step 1078. Following step 1076or 1078, processor 602 proceeds to step 1090 (described further below).

As the call progresses, changes in system traffic load, or drift betweenthe master clock to which cells 202 are synchronized and the masterclock to which mobile telephone switches 201 are synchronized, may causepacket receive times 1306 at channel elements 245 to drift out ofwindows 1302, as illustratively shown in FIG. 21, and may cause packetreceive times 1404 at processor 602 of SPU 264 to drift out of windows1402, as illustratively shown in FIG. 22. The drift due to changes insystem traffic load will tend to be in the same direction with respectto times 1306 and 1404: drift that advances time 1306 with respect towindow 1302 (shown in FIG. 21) will typically also advance time 1404with respect to window 1402 (not shown), whereas drift that retards time1404 with respect to window 1402 (shown in FIG. 22) will typically alsoretard time 1306 with respect to window 1302 (not shown). Conversely,the drift due to asynchrony between the master clocks will tend to be inopposite directions.

Drifting of times 1306 out of windows 1302 is detected by the channelelement's corresponding cluster controller 224. Its response thereto isshown in FIG. 16. Upon receipt of a packet at cluster controller 244,the routine of FIG. 16 is invoked, at step 1001, and it checks whetherthe received packet is the first traffic packet received for the call,at step 1002. Since the call is in progress, this will not be the firstreceived traffic packet, and the routine continues at step 1014. There,the routine compares the time at which the packet was received withwindow 1302, the same as at step 1004, to determine, at step 1016, whenin relation to window 1302 the packet was received. If the packet wasreceived within window 1302, no clock adjustment is necessary, and theroutine merely returns, at step 1022. If the packet was received priorto occurrence of window 1302, the routine causes the next traffic packetfor this call that is sent to processor 602 of the SPU 264 that ishandling the call to convey in its clock adjust field 322 a request toretard the time of the TX₋₋ INT₋₋ X interrupts for this call by one tick(e.g., one PCM speech sample time), at step 1018. Conversely, if thepacket was received after occurrence of window 1302, the routine causesthe next traffic packet for this call to convey in its clock adjustfield 322 a request to processor 602 to advance the time of the TX₋₋INT₋₋ X interrupts for this call by one tick, at step 1020. Followingstep 1018 or 1020, the routine returns to the point of its invocation,at step 1022.

Upon receipt of the traffic packet, processor 602 proceeds to make therequisite adjustment, at step 912 of FIG. 11. Drifting of times 1404 outof windows 1402 is detected by processor 602 itself. Processor 602 notesthe need for adjustment and the direction of adjustment, and proceeds tomake the requisite adjustment, tick-by-tick, also at step 912 of FIG.11.

When change in timing of processor 602 activity advances packet transmittimes 1305 from times 1305 to times 1505, and hence advances packetreceive times 1306 with respect to windows 1302, the result is newpacket receive times 1506 which are positioned back inside windows 1302,as shown in FIG. 21. When change in timing of processor 602 activityadvances windows 1402 and frame transmit times 1406 with respect totimes 1404, the result is new frame transmit times 1606 and packetreceive times 1404 which are positioned back inside windows 1402, asshown in FIG. 22.

The shift in the TX₋₋ INT₋₋ X and RX₋₋ INT₋₋ X signals output by circuit611 requires a corresponding shift to be made in the signal outputs ofclocks 621 and 622 of vocoder 604, thereby changing vocoder 604 trafficframe transmit times from times 1309 to times 1509 and changes vocoder604 traffic frame receive times from times 1409 to times 1609 in theexample of FIGS. 21 and 22, and thus realigning operations of vocoder604 with the time-shifted operations of processor 602. At the instant ofrealignment, however, vocoder 604 must present a traffic frame of calltraffic to processor 602 after vocoder 604 has had time to collecteither 159 or 161 PCM samples from circuit 605 instead of the normal 160samples corresponding to a 20 msec. time interval, and must output aframe of call traffic to circuit 605 within a time interval of either159 or 161 PCM samples instead of the normal 160, depending upon whetherthe adjustment is, respectively, to advance or to delay the interruptsignals. To compensate for this condition, when processor 602 commandscircuit 611 to effect the shifts in its TX₋₋ INT₋₋ and RX₋₋ INT₋₋ Xsignals for this service circuit 612 that are shown in FIGS. 21 and 22,respectively, at the same time processor 602 commands vocoder 604 ofthis same service circuit 612 to drop one PCM sample byte from its PCMoutput and to create an additional one PCM sample byte at its PCM input.Vocoder 604 does so, and the effect is to again align vocoder 604traffic frame input and output activities with PCM sample output andinput activities, respectively.

In the case of drift opposite to that shown in FIGS. 21 and 22, thesteps taken to compensate for the drift are the inverse of thosedescribed for FIGS. 21 and 22. Specifically, processor 602 commandscircuit 601 to retard its TX₋₋ INT₋₋ X and RX₋₋ INT₋₋ X interrupt signaloutputs for this service circuit 612 by one PCM sample interval, andcommands vocoder 604 to create an additional one PCM sample byte at itsPCM output and to drop one PCM sample byte from its PCM input.

These activities of processor 602 are diagramed in FIG. 18 at steps 1080et seq. As was stated previously, when processor 602 commences the clockadjustment activities of step 912 of FIG. 11, at step 1070, it checkswhether the just-received packet is the first traffic packet of thecall. While the call is in progress, a received packet will not be thefirst received packet, and so processor 602 proceeds to step 1080.There, processor 602 again compares the received packet's time stampwith receive window 1404 in order to determine, at step 1081, when thepacket was received in relation to the window. If the packet wasreceived within window 1404, no timing adjustment is necessary, and soprocessor 602 proceeds to step 1090. If the packet was received prior towindow 1404, processor 602 commands adaptive synchronization circuit 611to advance RX₋₋ INT₋₋ X signal for the corresponding service circuit 612by one tick, at step 1082, and commands vocoder 604 to decrease theoffset of its input clock 621 by one tick, at step 1083. Vocoder 604does so by causing clock 621 to reset after a count of 159 instead ofthe usual count of 160. But vocoder 604 still receives a full trafficframe of incoming call traffic holding the equivalent of 160 PCM samplebytes of information. So vocoder 604 discards one of those sample bytesto mask the timing realignment at its PCM output.

Returning to step 1081, if the packet is found to have been receivedafter window 1404, processor 602 commands adaptive synchronizationcircuit 611 to retard RX₋₋ INT₋₋ X signal for the corresponding servicecircuit 612 by one tick, at step 1084, and commands vocoder 604 toincrease the offset of its input clock 621 by one tick, at step 1085.Vocoder 604 does so by causing clock 621 to reset after a count of 161instead of the usual count of 160. But vocoder 604 still receives atraffic frame of incoming traffic holding the equivalent of 160 PCMsample bytes of information. So vocoder 604 generates an additionalsample byte to mask the timing realignment at its PCM output.

Following steps 1083 or 1085, processor 602 proceeds to step 1090.There, processor 602 examines clock adjust field 322 of the receivedtraffic frame to determine what clock adjustment, if any, has beenrequested by cell 202 that is handling the call. If an adjustment hasbeen requested, processor 602 commands adaptive synchronization circuit611 to adjust the time of occurrence of the TX₋₋ INT₋₋ X interrupts forthe call's corresponding service circuit 612 by one tick in therequested direction, at step 1091, and commands vocoder 604 to adjustthe offset of its output clock 621 by one tick in the same direction, atstep 1092. Vocoder 604 does so by causing clock 621 to reset after acount of 159 or 161 instead of the usual count of 160. Consequently,vocoder 604 accumulates either 159 or 161 PCM bytes of outgoing trafficsamples to supply to processor 602 in a frame holding 160 PCM samplebytes. To mask the timing realignment at its output to processor 602,vocoder 602 creates an additional PCM sample in the first instance anddiscards one of the PCM samples in the second instance. Following step1092, clock adjustment activities are completed, and processor 602returns, at step 1093, to the call processing activities of FIG. 11.

Alternatively, clocking adjustments may be made in multiples of one 125usec. ticks in order to achieve synchronization at a faster rate. Also,a combination of multiple-tick and single-tick adjustments (in different20 msec. cycles) could be used in order to control the speed with whichsynchronization may be achieved. Further, coarse adjustments (i.e.,involving multiple 125 usec. ticks) may be made in order to make majorsynchronization changes during a call. Said large adjustments areadvantageously made during the periods when speech activity is low.

At the start of a soft handoff, a channel element 245 of a second cell202 commences to handle the call in parallel with channel element 245 ofa cell 202 that has been handling the call alone until now. It is notknown a priori whether packet receive times 1306 at the second channelelement 245 will fall inside or outside of windows 1302 (see FIG. 19) orwhether packet receive times 1404 of packets sent by second channelelement 245 will fall inside or outside of windows 1402 (see FIG. 20) atprocessor 602, just as when the call is initially established. Ifreceive times 1306 and 1404 do fall outside of windows 1302 and 1402,respectively, for the second channel element 245, however, the clockadjustment technique of FIGS. 19 and 20 which was used when the call wasinitially established, cannot now be used. This is because the call isnow an established and ongoing call, and the use of that technique wouldresult in noticeable disruption--an audible "glitch"--in the call.Consequently, the more gradual but effectively "glitch-less" clockadjustment technique of FIGS. 21 and 22 is used to try and move receivetimes 1306 and 1404 within windows 1302 and 1402, respectively, for thesecond channel element 245. Multiple iterations of this adjustment mayneed to be performed in order to achieve the desired effect.

It is important to note, however, that the adjustment of FIGS. 21 and 22affects the receive times 1306 and 1404 for both of the channel elements245 that are handling the call. Consequently, it is possible that anadjustment which attempts to move times 1306 and 1404 into windows 1302and 1402 for the second channel element 245 will result in moving times1306 and 1404 out of windows 1302 and 1402 for the first channel element245.

It is imperative that times 1306 and 1404 of neither of the two channelelements 245 lag (i.e. occur after) their respective windows 1302 and1402. In contrast, times 1306 and 1404 that lead (i.e. occur before)their respective windows 1302 and 1402 can be compensated for bybuffering of the prematurely-received packets at channel element 245 andSPU 264. Consequently, if during soft handoff one channel element 245 isreporting a leading time 1306 while the other channel element 245 isreporting a lagging time 1306, the clock adjustment requests of thechannel element 245 which is reporting leading times 1306 are ignoredand only the requests of the other channel element 245 which isreporting lagging times 1306 are responded to by processor 602.

It is conceivable that differences in propagation delays betweenprocessor 602 and the two channel elements 245 that are involved in thesoft handoff are so great that packets sent by both channel elements 245during the same clock cycle of cell clock 1000 are received at processor602 during different clock cycles of processor 602 receive interruptclock RX₋₋ INT₋₋ X for that channel element 612, and that duplicatepackets sent by processor 602 during the same clock cycle of transmitinterrupt clock TX₋₋ INT₋₋ X to both channel elements 245 involved inthe soft handoff are received by those channel elements 245 duringdifferent clock cycles of cell clock 1000. To associate the receivedpackets with the proper clock cycles is the purpose of the sequencenumbers carried by sequence number field 320 of traffic frames 350 (seeFIG. 9). The association is done at steps 932-936 of FIG. 11.

As was alluded to previously, sequence numbers used by channel elements245 are calculated from, and hence bear a defined relationship to, clockcycles of cell clock 1000. Hence, during any clock cycle of cell clock1000, all channel elements 245 transmit packets having the same sequencenumber. Consequently, by comparing the sequence numbers of two receivedpackets, processor 602 can immediately determine whether both packetscorrespond to the same clock cycle of clock 1000, and if they do not,what their relative sequence is.

In the opposite direction of packet flow, from processor 602 to channelelements 245, no defined relationship exists between sequence number andclock cycle of cell clock 1000. However, at the beginning of the softhandoff, the channel element 245 that has been handling the call untilnow causes a message (HANDOFF₋₋ REQ; see discussion of FIG. 27, below)to be sent to the channel element 245 that is now commencing to handlethe call, which message reports the number of a recent cell clock 1000clock cycle and the sequence number of a packet which the first channelelement 245 has received during that clock cycle. Since sequence numbersare sequential, the second channel element 245 can easily compute fromthis received information which sequence numbers are associated withwhich subsequent clock cycles of cell clock 1000. The second channelelement 245 thus determines the cell clock 1000 clock cycle to which areceived packet corresponds.

It will now be explained in conjunction with FIGS. 23-35 how calls areset up, handed off, and torn down in the system of FIG. 2. Theillustrated activities take place as a result of exchanges of level-3packetized signalling messages, illustratively between pairs ofelements, e.g., SPU 264 to cells 202, cell 202 to ECP complex 134, orECP complex 134 to DCS controller 261. The Figures imply timingrelationships for message exchanges between the element pairs only, andnot across element pairs. All messages to and from ECP complex 134 areassumed to flow through control links 108; all packets between channelelements 245 and service circuits 612 are assumed to be frame-relayedthrough trunks 207 and 210.

FIG. 23 shows control signalling for setting up a packet-switched callpath for a call originating at a mobile telephone 203. Mobile telephone203 initiates the call by transmitting an ORIGINATION signal(illustratively one or more digital messages) conveying the calledtelephone number on an access channel. Over-the-air transmission orreception of signals is indicated in the Figures by a vertical segmentof a signal arrow. The ORIGINATION signal is received by channel element245 designated as a CDMA access channel in one of the cells 202, whichpasses it on in a message to its cluster controller 244, which forwardsit to controller 241 of its cell 202. Each controller 241 assigns a freeCDMA air channel to carry the call, and then passes the message alongwith identity of the assigned channel's corresponding channel elements245 on to ECP complex 134, in a conventional manner.

ECP complex 134 receives the CELL ORIGINATION message and selects a DCS201, a CIM 209, an SCM 220, and a service circuit 612 and a group oftrunks 106 of the selected speech coder module 220, to handle the call.ECP complex 134 then sends an MSC₋₋ FS₋₋ ASSIGNMENT message tocontroller 241 of the call-originating cell 202, conveying a DLCI of theselected service circuit 612. ECP complex 134 also sends a SETUP messageconveying the called telephone number and identifying selected module220, groups of trunks 106, and service circuit 612, to DCS controller261 that controls the selected module 220.

Controller 241 that receives the MSC₋₋ FS₋₋ ASSIGNMENT message forwardsthe message to cluster controller 244 of selected channel element 245.Cluster controller 244 conveys the information included in the messageto channel element 245 that has been selected to handle the call.Selected channel element 245 sets itself up to handle the call and thensends an FS₋₋ CONNECT packet 351 to the selected service circuit 612,using the frame-relay technique to transport the packet through theinterconnecting facilities' channels. Packet 351 uses the received DLCIof the selected service circuit 612 as the packet address in field 302,and conveys the DLCI of the selected channel element 245 in its datafield 304.

When processor 602 serving the selected service circuit 612 receives theFS₋₋ CONNECT packet, it returns an FS₋₋ ACK packet 351 to selectedchannel element 245 in acknowledgement of receipt of the FS₋₋ CONNECTpacket, using the DLCI contained in field 304 of the FS₋₋ CONNECT packetas the packet address in field 302 of the FS₋₋ ACK packet.Illustratively at this time processor 602 also sends to cell 202 allDLCIs that correspond to selected service circuit 612. Processor 602performs these tasks as part of LAPD processing at step 904 of FIG. 11.Processor 602 then stores the conveyed DLCI of selected channel element245 as part of the call state that is associated with selected servicecircuit 612, and marks the call state as corresponding to an activecall. A connection is now established between selected channel element245 and service circuit 612. Cluster controller 244 of the selectedchannel elements 245 next responds with an FS₋₋ CLOCK₋₋ ADJUST packet inwhich it conveys to processor 602 serving the selected serving circuitthe initial clock-adjustment information. This packet was discussed inconjunction with FIG. 16, steps 1001-1010. Processor 602 responds, byreturning an FS₋₋ ACK packets to cluster controller 244 and processingthe received packet in the manner discussed in conjunction with FIG. 17.A call path is now established between channel element 245 and servicecircuit 612, and they begin to exchange null traffic packets every 20msecs. until call traffic becomes available. Selected channel element245 responds to receipt of the second FS₋₋ ACK packet by causing aCHANNEL₋₋ CONFIRMATION message to be sent by its cell's controller 241to ECP complex 134 to advise it of completion of this end of theconnection.

DCS controller 261 that receives the SETUP message responds by causingcontroller 231 of the selected SCM 220 to seize a trunk 106 (DSOchannel) of the identified groups of trunks 106 and to outpulse thecalled telephone number on the seized trunk 106. The selected trunk 106corresponds to a particular time slot on TDM bus 130. Controller 261also causes translation and maintenance processor 609 of speechprocessing unit 264 which contains the selected service circuit 612 toconnect the abovementioned DSO channel from TDM bus 130 via TDM businterface 608 to that time slot of concentration highway 607 which isassigned to selected service circuit 612, thereby assigning that servicecircuit 612 to handle the subject call. Controller 261 then sends aCONNACK message to ECP complex 134 to advise it of successful completionof this end of the connection. When answer supervision is received fromtelecommunications facilities of network 100 over the selected trunk 106by controller 231, it notifies DCS controller 261, which in turn sendsan ANSWER message to ECP complex 134 to notify it of call completion.The call is now established fully through the system of FIG. 2, and calltraffic can flow between selected channel elements 245 through servicecircuit 612 and trunk 106 to and from the telecommunications facilitiesof network 100 and the call's destination.

FIG. 24 shows control signalling for setup of a call path for a calloriginating at public telephone network 100. Network 100 initiates thecall by seizing a trunk 106 and outpulsing thereon the digits of thecalled telephone number, in a conventional manner. Controller 231 of aspeech coder module 220 serving that trunk 106 detects the seizure onthe trunk's corresponding time slot of TDM bus 130 and collects thedialed digits, again conventionally, and then notifies DCS controller261. Controller 261 in turn notifies ECP complex 134 by sending it anINCALL message. The INCALL message conveys the called telephone number,and module 220 and trunk 106 I.D.s.

ECP complex 134 responds to the INCALL message by broadcasting to allcells 202 in the system of FIG. 2 an MSC₋₋ PAGE₋₋ REQUEST message. TheMSC₋₋ PAGE₋₋ REQUEST message identifies the called mobile 203 (e.g.,conveys the called phone number).

Controller 142 of each cell 202 responds to the MSC₋₋ PAGE₋₋ REQUESTmessage by conveying the MSC₋₋ PAGE₋₋ REQUEST message to a CDMAaccess-channel element 245 via cluster controller 244. Theaccess-channel element 245 responds by paging the called mobile 203, inthe manner specified for the CDMA arrangement.

When the called mobile 203 responds by transmitting a RESPONSE signal,one or more of the paging channel elements 245 receive the signal, andeach passes it on to its respective cluster controller 244. Clustercontrollers 244 forward the messages to controllers 241 of theirrespective cells 202. Controllers 241 of all cells 202 are continuallyexchanging messages (not shown) to update each other's databases oftheir respective status for existing and pending calls. Controllers 241of the respective cells 202 determine from these messages which cell 202is best suited to handle the call. Controller 241 of the selected cell202 then sends a CELL₋₋ PAGE₋₋ RESPONSE message on to ECP complex 134 tonotify complex 134 of that cell's selection to handle the call.

ECP complex 134 receives the CELL₋₋ PAGE₋₋ RESPONSE message and selectsa service circuit 612 of module 220 to which the call is connected tohandle the call at the other end of the call path. ECP complex 134 thensends an MSC₋₋ FS₋₋ ASSIGNMENT message to controller 241 of the selectedcell 202. The message is the same as described for the mobilecall-origination, and elicits the same response--to wit, an FS₋₋CONNECT, FS₋₋ ACK, FS₋₋ CLOCK₋₋ ADJUST, and FS₋₋ ACK packet exchangesequence between cell 202 and SPU 264, followed by a CHANNEL₋₋CONFIRMATION message from cell 202 to ECP complex 134, as described forFIG. 23. ECP complex 134 also sends a TONE₋₋ REQ message to DCScontroller 261 that controls the module 220 to which the call isconnected. Controller 261 responds by causing controller 231 of module220 to apply ringback to the trunk 106 that carries the call to and fromtelecommunications facilities of network 100.

Following sending of CHANNEL₋₋ CONFIRMATION message to ECP complex 134,selected channel element 245 transmits RINGING signals to called mobile203. When called mobile 203 responds with an ANSWER signal, selectedchannel element 245 causes an ANSWER message to be conveyed from itscell's controller 241 to ECP complex 134. ECP complex 134 responds bysending an ACCEPT message to DCS controller 261 of module 220 to whichthe call is connected. The message conveys the I.D. of service circuit612 that had been selected to handle the call. Controller 261 respondsby causing controller 231 to remove ringback tones from the call, andthen causing a connection to be made between the DSO channel carryingthe call on TDM bus 130 and selected service circuit 612, in the mannerdescribed for a mobile-originated call. Controller 261 then sends aCONNACK message to ECP complex 134 to advise it of successful completionof this end of the connection. The call path is now established fullythrough the system of FIG. 2, and packets bearing call traffic can flowbetween selected channel element 245 and the call's source, throughservice circuit 612.

FIG. 25 shows control signalling for call disconnection initiated bymobile telephone 203. Mobile telephone 203 initiates disconnection of anestablished call in which it is participating by transmitting a HANGUPsignal. This signal is received by channel element 245 which is handlingthe call. Channel element 245 responds by sending an FS₋₋ REMOVE packet351 to service circuit 612 which is handling the call, to advise it ofthe call disconnection.

Processor 602 responds to the FS₋₋ REMOVE packet by returning an FS₋₋ACK packet 351 to channel element 245 as part of the protocol processingof the FS₋₋ REMOVE packet, and by updating the call state for theservice circuit 612 which is handling the call to show that the call hasbeen disconnected. Traffic for the call now ceases to flow betweenchannel element 245 and service circuit 612, and channel element 245causes as RELEASE₋₋ MSC message to be sent by its cell's controller 241to ECP complex 134, to advise it of disconnection of this end of thecall path.

ECP complex 134 responds by sending a CLEAR message to DCS controller261 of speech coder module 220 that is handling the call, and by sendingan MSC₋₋ RELEASE₋₋ ACK message to controller 241 of cell 202 that washandling the call, to advise it that channel element 245 which had beenhandling the call is now free and available to handle a new call.Controller 261 responds to the CLEAR message by causing controller 231of module 220 to release trunk 106 that carries the call, and causingtranslation and maintenance processor 609 of the speech processing unit264 that contains service circuit 612 which is handling the call todisconnect the DSO channel which is carrying the call from theconcentration highway 607 time slot that is assigned to that servicecircuit 612. Controller 261 then sends a CLEAR₋₋ ACK message to ECPcomplex 105 to notify it that this end of the call path has also beendisconnected.

FIG. 26 shows control signalling for call disconnection initiated frompublic telephone network 100. Network 100 releases trunk 106 whichcarries the call. The release is detected by controller 231 of speechcoder module 220 that is handling the call, which notifies DCScontroller 261, and controller 261 in turn notifies ECP complex 134 bysending it a DISCONNECT message.

ECP complex 134 responds to receipt of the DISCONNECT message by sendingan MSC₋₋ NETWORK₋₋ RELEASE message through cell controller 241 andcluster controller 244 to channel element 245 that is handling the call.Channel element 245 responds by transmitting a RELEASE signal to mobiletelephone 203 that is involved in the call, and causing an FS₋₋ REMOVEpacket 351 to be sent to service circuit 612 that is handling the call.The FS₋₋ REMOVE signal is the same as described for the mobile-initiateddisconnection, and elicits the same response.

In response to receiving the RELEASE signal, mobile telephone 203 hangsup the call and transmits a HANGUP signal. This signal is received bychannel element 245 that is handling the call, and it responds bycausing a RELEASE₋₋ CONFIRMATION message to be sent by its cell'scontroller 241 to ECP complex 134, to inform it of disconnection of thisend of the call.

ECP complex 134 responds by sending a CLEAR message to DCS controller261 of speech coder module 220 that has been handling the call. TheCLEAR message is the same as described for the mobile-initiatedtermination, and elicits the same response.

FIGS. 27-29 show control signalling for soft handoff of the call fromone cell 202 to another. FIG. 27 shows signalling for the beginning ofsoft handoff, when a second cell 202, referred to as a slave cell,commences to handle the call jointly with cell 202 that had beenhandling the call until then, referred to as a master cell. A mobiletelephone 203 that is involved in a call monitors the strength of pilotchannel signals that it receives from a plurality of cells 202 includingmaster cell 202, and it periodically sends to master cell 202 aPWR.INFO. report on these received power levels. Channel element 245that is handling the call passes this report on to controller 241 ofmaster cell 202. On the basis of this information, and informationexchanged between the cells 202 themselves, controller 241 of mastercell 202 determines whether only master cell 202 should continue tohandle the call, or whether another cell 202 should be added to thecall. If controller 141 of master cell 202 determines that another cell202 should be added to the call, and that this slave cell 202 can handlethe call using CDMA and the same mobile channel as master cell 202,controller 241 of master cell 202 sends a HANDOFF₋₋ REQ message throughcontrol links 108 and IMS 104 to controller 241 of slave cell 202.HANDOFF₋₋ REQ message conveys the DLCIs of call-handling service circuit612 which are not used by master cell 202 for this call, and the I.D. ofthe mobile channel on which the call is being conducted.

Controller 241 of slave cell 202 receives the HANDOFF₋₋ REQ message andselects a channel element 245 of slave cell 202 and one of the receivedDLCIs of call-handling circuit 612 to handle the call. (Alternatively,the HANDOFF₋₋ REQ message may convey the DLCI of call-handling servicecircuit 612 which is used by master cell 202 for this call, andcontroller 241 of slave cell 202 merely toggles the value of theleast-significant bit of that DLCI which is contained in the message, tochange the DLCI value to a second DLCI that corresponds with servicecircuit 612 that is handling the call.) Controller 241 then forwards theselected DLCI along with other contents of the received message througha cluster controller 244 to selected channel element 245. Selectedchannel element 245 sets itself up to handle the call on the specifiedmobile channel, and then causes an FS₋₋ JOIN packet 351 to be sent toservice circuit 612 that is handling the call. This packet uses the DLCIof service circuit 612 which was received by selected channel element245 from controller 241 as the packet address in field 302, and conveysthe DLCI of selected channel element 245 in its data field 304.

When processor 602 serving service circuit 612 that is handling the callreceives the FS₋₋ JOIN packet, it returns an FS₋₋ ACK packet 351 toselected channel element 245 in acknowledgment of receipt of the FS₋₋JOIN packet, as part of LAPD processing at step 904 of FIG. 11.Processor 602 then stores the conveyed DLCI of selected channel element245 as part of the call state that is associated with service circuit612 that is handling the call, and marks the call state as being in softhandoff. A connection is now established between selected channelelement 245 of slave cell 202 and service circuit 612 that is handlingthe call, and they begin to exchange call traffic packets.

Channel element 245 of slave cell 202 responds to receipt of the FS₋₋ACK packet by causing a HANDOFF₋₋ ACK message to be sent by its cell'scontroller 241 via control links 108 and IMS 104 to controller 241 ofmaster cell 202 to advise it of completion of the connection. Controller241 of slave cell 202 also sends a HANDOFF₋₋ INFORMATION message to ECPcomplex 134 to notify it of the soft handoff, and ECP complex 134updates its database. Call traffic packets now flow between the oneservice circuit 612 and channel elements 245 of both master and slavecells 202 that are handling the call.

FIGS. 28 and 29 show signalling for the end of soft handoff, when one ofthe two cells 202 that is handling the call ceases to do so. Typically,though not necessarily, this will be the master cell 202. This scenariois shown in FIG. 28. During soft handoff, master and slave cells 202receive PWR.INFO. reports on pilot channel power levels measured bymobile telephone 203. Note that this PWR.INFO. is different from thepower control trend information which is received during soft handofffrom both cells 202 by processor 602 and is swapped between the twocells 202. Each cell 202 includes the received PWR.INFO. as reversesignalling in the next packet 350 that it sends to service circuit 612that is handling the call.

Processor 602 serving service circuit 612 that is handling the callreceives the PWR.INFO. as reverse signalling from both cells 202,selects and saves the PWR.INFO. from only one cell 202, at steps 968 ofFIG. 13 or 998 of FIG. 14, and then sends the stored PWR.INFO. back toboth cells 202, at steps 1216 and 1236 of FIG. 15. On account of theactions performed by processor 602, each cell 202 that is involved inthe handoff receives PWR.INFO. sent by the cell 202 that received betterquality signals from mobile 203. The received PWR.INFO. is forwarded tothe receiving cells' controllers 241.

Controllers 241 use this information to determine when one of themshould cease handling the call. When controller 241 of master cell 202determines that is should cease handling the call, it sends a HANDOFF₋₋DIRECTION signalling packet to processor 602 that serves thecall-handling service circuit 612. The packet indicates that handling ofthe call is being turned over to slave cell 202. Processor 602duplicates the signalling and returns it to both master and slave cells202, as shown in FIG. 15.

Upon receiving the HANDOFF₋₋ DIRECTION signalling, channel elements 245of both master and slave cells 202 transmit the HANDOFF₋₋ DIRECTIONinformation to mobile telephone 203 to appraise it thereof. Controller241 of master cell 202 then sends a MASTER₋₋ TRANSFER message viacontrol links 108 and IMS 104 to controller 241 of the other cell 202that is involved in the soft handoff, to notify it of completion of thehandoff and that it is to become the new master cell 202, and alsoforwards a copy of that information to channel element 245 of its owncell 202 which is handling the call. Channel element 245 responds byceasing to communicate call traffic to and from mobile telephone 203 andcausing an FS₋₋ REMOVE packet to be sent to service circuit 612 that ishandling the call to advise it of cessation of its involvement in thecall.

Processor 602 responds to the FS₋₋ REMOVE packet by returning an FS₋₋ACK packet to sending channel element 245 as part of the protocolprocessing of the FS₋₋ REMOVE packet, and by updating the call state forservice circuit 612 to shown that the call is no longer in soft handoff.Controller 241 of former master cell 202 receives the FS₋₋ ACK packetand responds by ceasing its cell's involvement in the call. Traffic forthe call ceases to flow between channel element 245 of former mastercell 202 and service circuit 612 that is handling the call, butcontinues to flow between service circuit 612 and channel element 245 ofthe former slave cell 202. Controller 241 of former master cell 202 nowsends a HANDOFF₋₋ INFORMATION message to ECP complex 134 to notify it ofcompletion of the handoff and the result thereof. ECP complex 134updates its database accordingly.

It will be noted that DCS controller 261 of the serving DCS 201 remainswholly uninvolved in the procedures of FIGS. 27 and 28, and that ECPcomplex 134 is also uninvolved except for being notified of thecompletions of the procedures. Consequently, the call-handling capacityof DCS controller 261 and ECP complex 134 is not adversely impacted bythe soft-handoff procedures.

FIG. 29 shows the scenario for soft-handoff completion wherein slavecell 202 ceases to serve the call 202 and master cell 202 continues toserve the call alone. Once again, the procedure begins with the masterand slave cells 202 providing pilot channel PWR.INFO. reports toprocessor 602 that serves the call-handling service circuit 612, andreturn to both cells 202 of the PWR.INFO. that was provided by the cell202 that is receiving better signals from mobile telephone 203. Whencontroller 241 of master cell 202 determines on the basis of these andother reports that slave cell 202 should cease handling the call, itsends a HANDOFF₋₋ DIRECTION signalling packet to processor 602 whichindicates that handling of the call is being regained by master cell202. Processor 602 duplicates the signalling and returns it to bothmaster and slave cells 202, again as shown in FIG. 15.

Upon receiving the HANDOFF₋₋ DIRECTION signalling, channel elements 245of both master and slave cells 202 transmit the HANDOFF₋₋ DIRECTIONinformation to mobile telephone 203 to appraise it thereof. Controller241 of master cell 202 then sends an INTRA/INTER₋₋ CELL HANDOFF₋₋ REMOVEmessage via control links 108 and IMS 104 to controller 241 of slavecell 202 to notify it of completion of the handoff and that it is todrop out of handling of the call. Controller 241 of slave cell 202notifies channel element 245 of slave cell 202 which is handling thecall. Channel element 245 responds in the same manner as was describedin conjunction with FIG. 28 for channel element 245 of master cell 202:by ceasing to communicate call traffic to and from mobile telephone 203and initiating an FS₋₋ REMOVE,FS₋₋ ACK packet exchange with processor602. Traffic flow ceases between channel element 245 of slave cell 202and service circuit 612 that is handling the call, but continues betweenservice circuit 612 and channel element 245 of master cell 202.Controller 241 of former slave cell 202 now sends a INTRA/INTER₋₋ CELL₋₋HANDOFF₋₋ ACK message to master cell 202, and a HANDOFF₋₋ INFORMATIONmessage to ECP complex 134, to notify them of completion of the handoffand the result thereof. ECP complex 134 updates its databaseaccordingly.

As in FIG. 28, there is little or no involvement of DCS controller 261and ECP complex 134 in this handoff-termination procedure.

FIG. 30 shows control signalling for call disconnection initiated bymobile telephone 203 while the call is in soft handoff. Mobile telephone203 initiates disconnection of the call by transmitting a RELEASEsignal. This signal is received by channel elements 245 which arehandling the call in both master and slave cells 202. Each channelelement 245 responds by sending cell-to-mobile reverse signallingconveying the RELEASE signal in the next packet 350 that it sends toservice circuit 612 that is handling the call.

Processor 602 serving that service circuit 612 receives the signallingfrom both cells 202 but saves only one copy, at step 968 of FIG. 13 or988 of FIG. 14, and returns the saved copy of the RELEASE signallingback to channel elements 245 of both master and slave cells 202 in thenext traffic packet, at steps 1216 or 1222 and 1236 of FIG. 15.Controller 241 of master cell 202 responds to return of the RELEASEsignalling by sending cell-to-mobile MOBILE₋₋ DISCONNECT forwardsignalling in the next packet 350 that is sent to service circuit 612that is handling the call.

Processor 602 serving that service circuit 612 receives and stores thesignalling, at step 956 of FIG. 13 or step 986 of FIG. 14, and thenreturns it to channel elements 245 of both master and slave cells 202 inthe next traffic packet, at steps 1222 and 1236 of FIG. 15. Channelelements 245 of both master and slave cells 202 each respond to receiptof the MOBILE₋₋ DISCONNECT signalling by transmitting a RELEASE signalto mobile telephone 203. Controller 241 of master cell 202 then sends acell-to-mobile signalling NULL₋₋ TRAFFIC command in the next packet toservice circuit 612. This command is returned to both cells 202 byprocessor 602, in the manner just described for MOBILE₋₋ DISCONNECTsignalling. Channel elements 245 of both master and slave cells 202 eachrespond to receipt of the NULL₋₋ TRAFFIC command by ceasing to transmitcall traffic and instead commencing to transmit null traffic to mobiletelephone 203. Both channel elements 245 also each cause an FS₋₋ REMOVEpacket 351 to be sent to service circuit 612 that is handling the call.The packets are the same as has been described previously, and elicitthe same responses from processor 602. Upon receipt of an FS₋₋ ACKpacket from processor 602, each cell's channel element 245 stopscommunicating with mobile telephone 203, and causes a RELEASE₋₋ MSCmessage to be sent by its cell's controller 241 to ECP complex 134 tonotify complex 134 that the corresponding cell 202 has ceased to handlethe call. ECP complex 134 updates its database correspondingly, andsends MSC₋₋ RELEASE₋₋ ACK messages to controllers 241 of master andslave cells 202. Following receipt of the second RELEASE₋₋ MSC message,ECP complex 134 also sends a CLEAR message to DCS controller 261 ofspeech coder module 220 that is handling the call. The message is thesame as described for FIG. 25 and elicits the same response from DCScontroller 261.

FIG. 31 shows control signalling for call disconnection initiated frompublic telephone network 100 while the call is in soft handoff. Network100 releases trunk 106 that carries the call. The release is detected bycontroller 231 of speech coder module 220 that is handling the call, andcontroller 231 notifies DCS controller 261, which in turn notifies ECPcomplex 134 by sending it a DISCONNECT message.

ECP complex 134 responds by sending an MSC₋₋ NETWORK₋₋ RELEASE messageto cell controllers 241 of master and slave cells 202. Controller 241 ofmaster cell 202 responds by sending cell-to-mobile forward signallingconveying a RELEASE signal in the next packet 350 that it sends toservice circuit 612 that is handling the call.

Processor 602 serving that service circuit 612 receives the RELEASEsignal and stores it, at step 956 of FIG. 13 or step 986 of FIG. 14, andthen sends the stored RELEASE signal to channel elements 245 of bothmaster and slave cells 202 in the next traffic packet, at steps 1222 and1236 of FIG. 15. Channel elements 245 of both master and slave cells 202each respond to the signalling information by transmitting a RELEASEsignal to mobile telephone 203 that is involved in the call.

In response to receiving the RELEASE signals transmitted by channelelements 245, mobile telephone 203 hangs up the call and transmits aMOBILE DISCONNECT signal as confirmation. This signal is received bychannel elements 245 of both master and slave cells 202. Each channelelement 245 that is handling the call responds thereto by causing a FS₋₋REMOVE packet 351 to be sent to service circuit 612 that is handling thecall. The packets are the same as has been described previously, andelicit the same responses from processor 602. Upon receipt of the FS₋₋ACK packet from processor 602, each channel element 245 responds bycausing a RELEASE₋₋ CONFIRMATION message to be sent to ECP complex 134to inform it of the call disconnection.

Following receipt of the second RELEASE₋₋ CONFIRMATION message, ECPcomplex 134 sends a CLEAR message to DCS controller 261 of speech codermodule 220 that is handling the call. The message is the same asdescribed for FIG. 25 and elicits the same response.

FIG. 32 shows control signalling for a semi-soft handoff of the callfrom one channel element 245 to another. A semi-soft handoff occursbetween channel elements 245 of either the same cell 202 or differentcells 202 connected to the same DCS 201, and involves a change in themobile channel that is carrying the call. As for soft handoff,controller 241 of cell 202 that is handling the call--the servingcell--monitors PWR.INFO. supplied by mobile telephone 203 to determinewhether serving channel element 245 should continue to do so, or whetherthe call should be handed off to a new channel element 245 in either thesame or a different--a new--cell 202. If controller 241 of serving cell202 determines that it should hand off the call to a new channel element245, and that new cell 202 can handle the call using CDMA, controller241 of serving cell 202 sends a HANDOFF₋₋ REQ message through controllinks 108 and IMS 104 to controller 241 of new cell 202. (If servingcell 202 and new cell 202 are the same cell, this message is not sentoutside of the cell.) The message is the same as described for softhandoff, and elicits the same response from new cell 202 as it does froma slave cell 202. However, because new channel element 245 does notoperate on the same mobile channel as mobile telephone 203 and servingchannel element 245, new channel element 245 is not in communicationwith mobile telephone 203 and only null traffic packets flow from newchannel element 245 to service circuit 612 that is handling the call.

The HANDOFF₋₋ ACK message that is sent by new cell 202 back to servingcell 202 specifies the mobile channel on which new channel element 245operates. Controller 241 of serving cell 202 receives the HANDOFF₋₋ ACKmessage and responds thereto by causing serving channel element 245 totransmit a signal to mobile telephone 203 telling it to switch itsoperations to the mobile channel on which new channel element 245operates. When mobile telephone 203 does so, traffic begins to flowbetween mobile telephone 203, new channel element 245, and servicecircuit 612, but ceases to flow between mobile telephone 203 and servingchannel element 245, and only null traffic packets commence to flow fromserving channel element 245 to service circuit 612.

New channel element 245 responds to commencement of receipt of calltraffic from mobile telephone 203 by causing a HANDOFF₋₋ INFORMATIONmessage to be sent to ECP complex 134, and an INTERCELL₋₋ HANDOFFmessage to be sent to serving cell 202, to notify them of the handoff.ECP complex 134 updates its database, while controller 241 of servingcell 202 causes the cell to drop out of serving the call. Specifically,channel element 245 of serving cell 202 causes an FS₋₋ REMOVE packet tobe sent to service circuit 612 that is serving the call. The packet isthe same as discussed previously and elicits the same response. Trafficthus ceases to flow between serving channel element 245 and servicecircuit 612. Serving channel element 245 responds to receipt of the FS₋₋ACK packet from service circuit 612 by causing a HANDOFF₋₋ INFORMATIONmessage to be sent to ECP complex 134 to notify it of handoffcompletion, and ECP complex 134 updates its database.

Once again, it will be noted that DCS controller 261 of the serving DCS201, remains wholly uninvolved in the procedure of FIG. 31, and that ECPcomplex 138 is also uninvolved except for being notified of thecompletion of the procedure. Consequently, the call-handling capacity ofcontroller 261 and ECP complex 134 is not adversely impacted by thesemi-soft handoff procedure.

FIG. 33 shows control signalling for a hard handoff from one CDMA cell202 to another. In CDMA, hard handoff does not necessarily involve achange in the mobile channel, but it does involve a change in thedigital cellular switch 201 (see FIG. 2) which is handling the call.

As for soft and semi-soft handoff, controller 241 of cell 202 that ishandling the call--referred to as serving cell 202--monitors PWR.INFO.supplied by mobile telephone 203 and uses it along with other statusinformation to determine whether serving cell 202 should continue tohandle the call, or whether it should hand the call off to another cell202--referred to as new cell 202--that is connected to a differentmobile telephone switch 201 than serving cell 202. If controller 241 ofserving cell 202 determines to hand off the call, it sends a HARD₋₋HANDOFF₋₋ REQUEST message to ECP complex 134. The message identifies thecall, the proposed new cell 202, and the mobile channel that is beingused for the call by serving cell 202.

ECP complex 134 responds to the message by determining which DCS 201 isconnected to new cell 202, and selecting a new speech coder module 220within that DCS 201 and as service circuit 612 of the new module 220 tohandle the call. ECP complex 134 then selects a trunk 206 connectingserving speech coder module 220 of serving DCS 201 with new speech codermodule 220 of new DCS 201, and sends a SETUP message to controller 261of serving DCS 201 identifying the selected new speech coder module 220,service circuit 612, and trunk 206, and also identifying the trunk 106of serving speech coder module 220 which carries the call.

Controller 261 of serving DCS 201 receives the SETUP message andresponds by causing controller 231 of serving module 220 to seize theidentified trunk 206, to outpulse thereon identification of the selectedmodule 220 and service circuit 612, and to connect call-carrying trunk106 to trunk 206 in a conferencing arrangement. This results in seizureof trunk 206 at new module 220 and collection by new module's controller231 of the outpulsed identification. Controller 261 of serving DCS 201then sends a CONNACK message to ECP complex 134 to advise it ofestablishment of the connection between serving and new modules 220,while controller 231 of new module 220 sends the collected outpulsedinformation to controller 261 of new DCS 201, which sends an INCALLmessage conveying the collected outpulsed information to ECP complex 134to advise it of the incoming call.

ECP complex 134 associates the received CONNACK and INCALL messages onthe basis of their contents; the messages serve as confirmation to ECPcomplex 134 that TDM buses 130 of new and serving modules 220 are nowinterconnected through trunk 206. ECP complex 134 then sends a MSC₋₋NEW₋₋ HANDOFF message to controller 241 of new cell 202. This messagenotifies new cell 202 that it has been selected to handle the call, andconveys to it the identification of the mobile channel that is presentlycarrying the call. New cell controller 241 responds by determiningwhether new cell 202 can handle the call, and if so, on which mobilechannel. New cell controller 241 then sends a CHANNEL₋₋ ACTIVATION₋₋CONFIRMATION message conveying this information back to ECP complex 134.Assuming that new cell 202 can handle the call, ECP complex 134 sends tonew cell controller 241 an MSC₋₋ FS₋₋ ASSIGNMENT message conveying theDLCIs of the service circuit 612 of new module 220 which has beenselected to handle the call. This message is the same as discussedpreviously in conjunction with FIG. 23, and elicits the same responses.New cell 202 returns an FS₋₋ CONFIRMATION message to ECP complex 134,and ECP complex 134 in turn sends an MSC₋₋ OLD₋₋ HANDOFF message toserving cell 202, advising them of completion of the connection betweennew channel element 245 and new service circuit 612, and the mobilechannel on which new channel element 245 operates.

ECP complex 134 responds to the FS₋₋ CONFIRMATION message by sending anACCEPT message to controller 261 of new DCS 201. Controller 261 of newDCS 201 responds by causing controller 231 of new module 220 to makeconnection between new service circuit 612 and trunk 206 connecting newmodule 220 to serving module 220, in the manner described previously forACCEPT messages. This results in the output of both new and servingservice circuits 612 being connected to the same time slot of TDM bus130 of serving speech coder module 220, in a conference arrangement. Ifboth new and serving channel elements 245 are operating on the samemobile channel, this results in superimposition of duplicate outputs onthe same time slot, and thus has substantially no effect on thetime-slot contents. If the two channel elements 245 are not operating onthe same mobile channel, this results in superimposition of real trafficand null traffic samples--speech or data, and silence--on the same timeslot, and thus again has substantially no effect on the time-slotcontents. Controller 261 of new DCS 201 then returns a CONNACK messageto ECP complex 134 to advise it of completion of the connection.Controller 231 of serving module 220 detects completion of theconnection and notifies controller 261 of serving DCS 201, which returnsan ANSWER message to ECP complex 134 to notify it thereof.

Serving cell controller 241 responds to MSC₋₋ OLD₋₋ HANDOFF message thatit receives from ECP complex 134 by checking the message contents todetermine if new channel element 245 is operating on the same mobilechannel as serving channel element 245. If not, serving cell controller241 causes serving channel element 245 to transmit a signal to mobiletelephone 203 commanding it to switch operation from the mobile channelthat it is now using to the mobile channel used by new channel element245, as shown in dashed lines in FIG. 33. When mobile telephone 203 doesso, traffic flow is switched from serving cell 202 to new cell 202, asshown in dashed lines.

Channel element 245 of new cell 207 responds to commencement of receiptof the call traffic by causing new cell controller 241 to send aHANDOFF₋₋ VOICE₋₋ CHANNEL₋₋ CONFIRMATION message to ECP complex 134.This message advises ECP complex 134 of success of the handoff. ECPcomplex 134 responds by sending an MSC₋₋ CHANNEL₋₋ DEACTIVATION messageto serving cell 202 and a CLEAR message to controller 261 of serving DCS201 to cause serving cell 202 and serving SPU 264 to drop out ofhandling of the call.

Controller 241 of serving cell 202 forwards the MSC₋₋ CHANNEL₋₋DEACTIVATION message to serving channel element 245, which responds bycausing an FS₋₋ REMOVE packet to be relayed to serving service circuit612. The packet is the same as described previously, and elicits thesame response. When serving cell 202 has ceased to handle the call, itscontroller 241 sends an FS₋₋ CONFIRMATION message to ECP complex 134 toadvise it thereof.

Controller 261 of serving DCS 201 passes the received CLEAR message tocontroller 231 of serving module 220. Controller 231 responds by causingtranslation and maintenance processor 609 of speech processing unit 264which contains serving service circuit 612 to disconnect the call (i.e,the time slot of TDM bus 130 which is carrying the call) from theconcentration highway 607 time slot that is assigned to that servicecircuit 612. However, because new service circuit 612 of new module 220is now connected to trunk 106 that carries the call to and from TDM bus130 of serving module 220 via trunk 206, controller 231 of servingmodule 220 does not release that trunk 106 and TDM bus 130 time slot.Controller 261 of serving DCS 201 then sends a CLEAR₋₋ ACK message toECP complex 134 to advise it that serving SPU 264 of serving module 220has ceased to serve the call. Receipt of both the CLEAR₋₋ ACK and FS₋₋CONFIRMATION messages indicates to ECP complex 134 that the handoff hasbeen completed.

FIGS. 34-35 show control signalling for a hard handoff from a CDMA radio243 of a serving cell 202 to a conventional analog radio 143 of a newcell 102 or 202. FIG. 34 shows control signalling for the handoffbetween two cells connected to the same DCS 201, while FIG. 35 shows thehandoff between two cells connected to different DCSs 201.

Considering FIG. 34, a conventional mobile telephony cell 102 may beequipped with a CDMA pilot channel. If it is, control communicationsproceed with a new cell 102 as they would with a new cell 202, and areshown in FIG. 33; if new cell 102 is not equipped with a CDMA pilotchannel, the control communications shown in FIG. 34 for new cell 102instead also proceed with serving cell 202. In other words, if new cell102 is not equipped with a CDMA pilot channel, conversion of the call toconventional mobile telephony occurs on serving cell 202, and only thenis the call handed off from serving cell 202 to new cell 102, in theconventional hard-handoff manner.

As for handoff types discussed previously, controller 241 of servingcell 202 monitors PWR.INFO. supplied by mobile telephone 203 todetermine whether or not to hand the call off to another cell. Ifcontroller 241 of serving cell 202 determines that it should handoff thecall to a conventional radio 143 in a cell 202 or 102, and the new cell202 or 102 is connected to the same mobile telephone switch 201 asserving cell 202, controller 241 sends an ANALOG₋₋ HANDOFF₋₋ REQUESTmessage to ECP complex 134. The message identifies the proposed new cell102 or 202. ECP complex 134 responds by selecting a trunk 109 of aswitching module 120 or 220 to which new cell 102 or 202 is connected,and sending an MSC₋₋ NEW₋₋ HANDOFF message to controller 141 or 241 ofnew cell 102 or 202. The message identifies the selected trunk 109 andqueries if new cell 102 or 202 can handle the call. Controller 141 or241 of new cell 102 or 202 replies with a CHANNEL₋₋ ACTIVATION₋₋CONFIRMATION message to ECP complex 134 identifying the conventionalmobile channel on which it will handle the call, and also connects thatmobile channel to the selected trunk 109. ECP complex 134 responds byselecting a trunk 109 that is connected to serving module 220, and sendsa CONNECT message to DCS controller 261 of serving DCS 201 identifyingnew module 120 or 220 to which new cell 102 or 202 is connected, theselected trunk 109 that is connected to new module 120 or 220, and theselected trunk 109 outgoing from serving speech coder module 220.

DCS controller 261 of serving DCS 201 receives the CONNECT message andresponds by causing controller 231 of serving module 220 to connect thecall (the TDM bus 130 time slot) to the identified outgoing trunk 109 ina conference arrangement, and causing TMS 121 to connect the twoidentified trunks 109 to each other. Controller 261 of serving DCS 201then sends a CONNACK message to ECP complex 134 to advise it ofcompletion of the connection between the serving and the new modules.

ECP complex 134 responds by sending an MSC₋₋ OLD₋₋ HANDOFF message tocontroller 241 of serving cell 202 conveying the mobile channel on whichthe new cell 102 or 202 will handle the call. In response, controller241 causes serving channel element 245 to transmit a signal to mobiletelephone 203 commanding it to switch to conventional mobile telephonyoperation and to use the mobile channel that was specified in the MSC₋₋NEW₋₋ HANDOFF message.

When mobile telephone 203 does so and commences transmitting on the newmobile channel, new cell 102 or 202 receives the transmissions andnotifies ECP complex 134 via a HANDOFF₋₋ VOICE₋₋ CHANNEL₋₋ CONFIRMATIONmessage. ECP complex 134 responds with an MSC₋₋ CHANNEL₋₋ DEACTIVATIONmessage to serving cell 202 and a CLEAR message to DCS controller 261 ofserving DCS 201, to cause serving cell 202 and serving SPU 264 to dropout of handling of the call. The messages are the same as discussed forCDMA-to-CDMA hard handoff, and elicit the same responses. As in thatcase, receipt of both the CLEAR₋₋ ACK and FS₋₋ CONFIRMATION messagesindicates to ECP complex 134 that the handoff has been completed.

Referring now to FIG. 35, the handoff to a new cell 102 or 202 connectedto a different switch 101 or 201 than serving cell 202 starts out thesame way as shown in FIG. 34. But following a decision to hand off thecall to a cell 102 served by a new DCS 101 or 201, controller 241 ofserving cell 202 sends a ANALOG₋₋ HANDOFF₋₋ REQUEST message to ECPcomplex 134 to request the handoff. The message identifies the proposednew cell 102 or 202. ECP complex 134 responds to this message bydetermining which switch 101 or 201 is connected to new cell 102 or 202,and selecting a new switching module 120 or 220 of that switch 101 or201 and a trunk 106 connected to that selected module 120 or 220 tohandle the call. ECP complex 134 then selects an outgoing trunk 106connected to serving module 220 and sends a SETUP message to DCScontroller 261 of serving DCS 201 identifying the selected new module120 or 220 and its connected trunk 106, the trunk 106 outgoing fromserving speech coder module 220, and the trunk 106 of serving speechcoder module 220 which carries the call.

The SETUP message is analogous to that described in conjunction withFIG. 33, and elicits like responses. Hence, the handoff proceeds asdescribed for FIG. 33. However, no SPU 264 will be involved in handlingthe call at new DCS 101 or 201, so instead of sending an FS₋₋ ASSIGNmessage to new cell 102 or 202 as in FIG. 33, ECP complex 134 insteadproceeds directly to send an ACCEPT message to DCS controller 161 or 261of new DCS 101 or 201. DCS controller 161 or 261 responds by causingcontroller 131 of new module 120 or controller 251 of a cellinterconnect module 209 to connect the selected trunk 106 of new module120 or 220 to the call (i.e., to the call's corresponding time slot oreither TDM bus 130 of module 120 or TDM bus 230 of CIM 209), therebyestablishing a connection between that selected trunk 106 and new cell102 or 202. Akin to FIG. 33, this results in the output of both new cell102 or 202 and serving cell 202 being connected to the same time slot ofTDM bus 130 of serving speech coder module 220. DCS controller 161 or261 of new DCS 101 or 201 then returns a CONNACK message to ECP complex134 to advise it of completion of the connection, while controller 231of serving module 220 detects completion of the connection and notifiesserving DCS controller 261, which responds by returning an ANSWERmessage to ECP complex 134.

ECP complex 134 responds to receipt of the CONNACK message by sending anMSC₋₋ OLD₋₋ HANDOFF message to controller 241 of serving cell 202. Themessage is the same as discussed in conjunction with FIG. 34, andhenceforth the handoff proceeds the same as described for FIG. 34, untilhandoff completion.

Of course, it should be understood that various changes andmodifications to the illustrative embodiment described above will beapparent to those skilled in the art. For example, different packettransmission techniques, such as Asynchronous Transfer Mode (ATM) can beused. Or, the partitioning of functionality between the control entitiesof the cells, ECP complex, and the digital cellular switches can bechanged. Also, modules within a digital cellular switch (both CIMs 209and SCMs 220) may be interconnected by a center-stage switch instead ofjust directly by trunks. Furthermore, the system described above can beapplied to pseudo-synchronous wireless-access systems other than mobiletelephony--for example, to personal communications networks (PCNs). Suchchanges and modifications can be made without departing from the spiritand the scope of the invention and without diminishing its attendantadvantages. It is therefore intended that all such changes andmodifications be covered by the following claims.

We claims:
 1. An apparatus comprising:a first operating unit having its operations synchronized with first clock signals; a second operating unit having its operations synchronized with second clock signals which are asynchronous with the first clock signals; a third operating unit for interfacing the operations of the first unit with the operations of the second unit, the third unit having its operations nominally synchronized with the operations of the first unit; means for monitoring an extent of asynchrony between the operations of the second and the third units, to determine whether the extent of asynchrony lies outside of a predetermined range of allowed asynchrony; and means responsive to a determination that the extent of asynchrony does lie outside of the predetermined range, for adjusting the synchronization of the operations of the third unit with the operations of the first unit, to move the extent of asynchrony between the operations of the second and the third units to within the range.
 2. An apparatus comprising:first operating unit having its operations synchronized with first timing signals having a nominal frequency and a first phase; second operating unit having its operations synchronized with second timing signals having the nominal frequency and a second phase different from and fluctuating with respect to the first phase; third operating unit for interfacing the operations of the first unit with the operations of the second unit and having its operations synchronized with third timing signals having the nominal frequency and a third phase offset by an adjustably fixed amount from the first phase; means for determining whether the third phase falls outside of a predetermined range of allowed offset from the second phase; and means responsive to a determination that the third phase falls outside of the predetermined range, for adjusting the fixed offset of the third phase from the first phase to move the third phase within the range.
 3. A communications system comprising:a first unit for receiving incoming communication traffic at times dictated by first clock signals having a nominal frequency and a first phase; a second unit for transmitting incoming communication traffic at times dictated by second clock signals having the nominal frequency and a second phase different from and fluctuating with respect to the first phase; a third unit for interfacing communications between the first and the second units by transmitting to the first unit incoming communication traffic received from the second unit at times dictated by third clock signals having the nominal frequency and having a third phase that is offset by an adjustable fixed amount from the first phase; first means for determining whether the third unit receives incoming communication traffic from the second unit within predetermined windows of time prior to the times of transmission by the third unit of the received incoming communication traffic; and second means responsive to a determination that receptions of the incoming communication traffic at the third unit fall outside of the windows for either increasing or decreasing the amount of the offset of the third phase from the first phase to move the receptions into the windows.
 4. The system of claim 3 wherein:the second means adjust the offset at commencing of a communication in one step by any amount required to move the receptions substantially into centers of the windows, and adjust the offset during the communication in a series of sequential steps.
 5. The system of claim 3 further comprising:third means cooperative with the second means for inserting additional traffic into the incoming communication traffic received by the third unit and transmitting the additional traffic to the first unit while the amount of the offset is being increased, and for deleting a portion of the incoming communication traffic received by the third unit from the incoming communication traffic transmitted to the first unit while the amount of the offset is being decreased.
 6. A communications system comprising:a first unit for transmitting outgoing communication traffic at times dictated by first clock signals having a nominal frequency and a first phase; a second unit for transmitting outgoing communication traffic at times dictated by second clock signals having the nominal frequency and a second phase different from and fluctuating with respect to the first phase; a third unit for interfacing communications between the first and the second units by transmitting to the second unit outgoing communication traffic received from the first unit at times dictated by third clock signals having the nominal frequency and having a third phase that is offset by an adjustably fixed amount from the first phase; first means for determining whether the second unit receives outgoing communication traffic from the third unit within predetermined windows of time prior to the times of transmission by the second unit of the received outgoing communication traffic; and second means responsive to a determination that receptions of the outgoing communication traffic at the second unit fall outside of the windows for either increasing or decreasing the amount of the offset of the third phase from the first phase to move the receptions into the windows.
 7. The system of claim 6 wherein:the second means adjust the offset at commencing of a communication in one step by any amount required to move the receptions substantially into centers of the windows, and adjust the offset during the communication in a series of sequential steps.
 8. The system of claim 6 further comprising:third means cooperative with the second means for inserting additional traffic into the outgoing communication traffic transmitted from the first unit and causing the third unit to receive the additional traffic while the amount of the offset is being increased, and for deleting a portion of the outgoing communication traffic transmitted by the first unit from the outgoing communication traffic received by the third unit while the amount of the offset is being decreased.
 9. A communications system comprising:a first unit for transmitting outgoing communication traffic and receiving incoming communication traffic at times dictated by first clock signals having a nominal frequency and a first phase; a second unit for transmitting received incoming and outgoing communication traffic at times dictated by second clock signals having the nominal frequency and a second phase different from and fluctuating with respect to the first phase; a third unit for interfacing communications between the first and the second units by transmitting to the second unit outgoing communication traffic received from the first unit at times dictated by third clock signals having the nominal frequency and having a third phase that is offset by an adjustably fixed first amount from the first phase, and by transmitting to the first unit incoming communication traffic received from the second unit at times dictated by fourth clock signals having the nominal frequency and having a fourth phase that is offset by an adjustably fixed second amount from the first phase; first means for determining whether the second unit receives outgoing communication traffic from the third unit within first predetermined windows of time prior to the times of transmission by the second unit of the received outgoing communication traffic; second means for determining whether the third unit receives incoming communication traffic from the second unit within second predetermined windows of time prior to the times of transmission by the third unit of the received incoming communication traffic; third means responsive to a determination that either receptions of the outgoing communication traffic at the second unit fall outside of the first windows or receptions of the incoming communication traffic at the third unit fall outside of the second windows for either increasing or decreasing the amount of the offset of either the third phase or the fourth phase from the first phase to move the receptions that fall outside of their corresponding windows into the corresponding windows.
 10. The system of claim 9 wherein:the third means are responsive to a determination by the first means that receptions of the outgoing communication traffic at the second unit lag the first windows, for decreasing the amount of the offset of the third phase from the first phase.
 11. The system of claim 10 wherein:the third means are further responsive to a determination by the first means that receptions of the outgoing communication traffic at the second unit lead the first windows, for increasing the amount of the offset of the third phase from the first phase.
 12. The system of claim 9 wherein:the third means are responsive to a determination by the second means that receptions of the incoming communication traffic at the third unit lag the second windows, for increasing the amount of the offset of the fourth phase from the first phase.
 13. The system of claim 12 wherein:the third means are further responsive to a determination by the second means that receptions of the incoming communication traffic at the third unit lead the second windows, for decreasing the amount of the offset of the fourth phase from the first phase.
 14. The system of claim 9 wherein:the third means adjust the first amount and the second amount of offset at commencing of a communication each in one step by any amount required to move the receptions that fall outside of their corresponding windows into the corresponding windows, and adjust the first amount and the second amount of offset during the communication in a series of sequential steps by an integral multiple of a same predetermined amount during each step.
 15. The system of claim 9 further comprising:fourth means cooperative with the third means for inserting additional traffic into the outgoing communication traffic transmitted from the first unit and causing the third unit to receive the additional traffic while the amount of the offset of the third phase is being increased and deleting a portion of the outgoing communication traffic transmitted by the first unit from the outgoing communication traffic received by the third unit while the amount of the offset of the third phase is being decreased, and for inserting additional traffic into the incoming communication traffic received by the third unit and transmitting the additionaal traffic to the first unit while the amount of the offset of the fourth phase is being increased and deleting a portion of the incoming communication traffic received by the third unit from the incoming communication traffic transmitted to the first unit while the amount of the offset of the fourth phase is being decreased.
 16. The system of claim 9 wherein:the first unit is for transmitting a stream of outgoing communication traffic and receiving a stream of incoming communication traffic; the second unit is for transmitting packets of received incoming communication traffic, and receiving packets of outgoing communication traffic for transmission of the outgoing communication traffic; the third unit includes fourth means responsive to receipt of the stream of outgoing communication traffic from the first unit for packetizing the received outgoing communication traffic and transmitting the packets of the received outgoing communication traffic to the second unit at times dictated by the third clock signals, and fifth means responsive to receipt of the packets of the incoming communication traffic from the second unit for depacketizing the received incoming communication traffic and transmitting the depacketized received incoming communication traffic toward the first unit at times dictated by the fourth clock signals; the first means are for determining whether the second unit receives the packets of outgoing communication traffic from the third unit within the first predetermined windows; and the second means are for determining whether the third unit receives the packets of incoming communication traffic from the second unit within the second predetermined windows.
 17. A call-traffic processing apparatus for a cellular radio-telephone system that includes the apparatus, at least one cell each for transmitting first packets containing first frames of coded incoming call traffic received from a radio telephone to the apparatus and for transmitting to the radio telephone outgoing call traffic received from the apparatus in second packets containing second frames of coded outgoing call traffic, and a mobile-telephone switching system for interconnecting cells with each other and with a telephone network by routing a first digital stream of cells with each other and with a telephone network by routing a first digital stream of incoming call traffic received from the apparatus to a destination and by routing a second digital stream of outgoing call traffic received from a source to the apparatus, and wherein the first and the second digital streams are synchronized with first clock signals having a nominal frequency and a first phase and derived from the telephone network and the transmissions of the incoming and the outgoing call traffic by the cell are synchronized with second clock signals having the nominal frequency and a second phase that is different from and fluctuates with respect to the first phase, the call-traffic processing apparatus comprising:outgoing vocoder means for receiving the second digital stream of outgoing call traffic synchronously with the first clock signals, coding the received outgoing call traffic, and transmitting second frames of the coded outgoing call traffic synchronously with third clock signals having the nominal frequency and a third phase that is offset by an adjustably fixed first amount from the first phase, incoming vocoder means for receiving first frames of the coded incoming call traffic synchronously with fourth clock signals having the nominal frequency and a fourth phase that is offset by an adjustably fixed second amount from the first phase, decoding the received incoming call traffic, and transmitting the second digital stream of incoming call traffic synchronously with the first clock signals; outgoing processing means for receiving the second frames of the coded outgoing call traffic from the outgoing vocoder means, packetizing the received second frames into the second packets, and transmitting the second packets to the cell synchronously with fifth clock signals having the nominal frequency and a fifth phase that is offset by an adjustably fixed third amount from the first phase; incoming processing means for receiving the first packets from the cell, depacketizing the received first packets into the first frames, and transmitting the first frames to the incoming vocoder means synchronously with sixth clock signals having the nominal frequency and a sixth phase that is offset by an adjustably fixed fourth amount from the first phase; clock signal generating means for deriving the third, the fourth, the fifth, and the sixth clock signals from the first clock signals; first means for determining whether the incoming processing means receive the first packets within first predetermined windows of time prior to the times of transmission of the first frames by the incoming processing means to the incoming vocoder means; second means for determining whether the cell receives the second packets within second predetermined windows of time prior to the times of transmission by the cell of the received outgoing call traffic to the mobile telephone; and third means responsive to a determination that either receptions of the first packets fall outside of the first windows or receptions of the second packets fall outside of the second windows for causing the clock signal generating means to either increase or decrease the amounts of the offsets of either both the third and the fifth phases or both the fourth and the sixth phases, with respect to the first phase, to move the packet receptions that fall outside of their corresponding windows into the corresponding windows.
 18. The apparatus of claim 17 wherein:the third means are responsive to a determination by the first means that receptions of the first packets at the incoming processing means lag the first windows, for causing the clock signal generating means to increase the amounts of the offsets of both the fourth and the sixth phases from the first phase by a same amount.
 19. The apparatus of claim 18 wherein:the third means are responsive to a determination by the first means that receptions of the first packets at the incoming processing means lead the first windows, for causing the clock signal generating means to decrease the amounts of the offsets of both the fourth and the sixth phases from the first phase by a same amount.
 20. The apparatus of claim 17 wherein:the third means are responsive to a determination by the second means that receptions of the second packets at the packets at the cell lag the second windows, for causing the clock signal generating means to decrease the amounts of the offsets of both the third and the fifth phases from the first phase by a same amount.
 21. The apparatus of claim 20 wherein:the third means are responsive to a determination by the second means that receptions of the second packets at the cell lead the second windows, for causing the clock signal generating means to increase the amounts of the offsets of both the third and the fifth phases from the first phase by a same amount.
 22. The apparatus of claim 17 wherein:the third means cause the clock signal generating means to adjust either the first and the third amounts of offset or the second and the fourth amounts of offset, in one step by any amount required to move any packet receptions that fall outside of their corresponding windows into the corresponding windows at a commencing of a communication, and cause the clock signal generating means to adjust either the first and the third amounts of offset or the second and the fourth amounts of offset by an integral multiple of a same predetermined amount in each step of a series of sequential steps to move packet receptions that fall outside of their corresponding windows into the corresponding windows during the communication.
 23. The apparatus of claim 17 further including:means cooperative with the third means for causing the outgoing vocoder means to insert traffic additional to the outgoing call traffic received by the outgoing vocoder means into second frames transmitted by the outgoing vocoder means while the amounts of the offsets of the third and the fifth phases are being increased, causing the outgoing vocoder means to delete a portion of the outgoing call traffic received by the outgoing vocoder means from the second frames transmitted by the outgoing vocoder means while the amounts of the offsets of the third and fifth phases are being decreased, causing the incoming vocoder means to insert traffic additional to the incoming call traffic received by the incoming vocoder means into the first digital stream transmitted by the incoming vocoder means while the amounts of the offsets of the fourth and the sixth phase are being increased, and causing the incoming vocoder means to delete a portion of the incoming call traffic received by the incoming vocoder means from the first digital stream transmitted by the incoming vocoder means while the amounts of the offsets of the fourth and the sixth phase are being decreased.
 24. A method of operating an apparatus that comprises a first operating unit, a second operating unit, and a third operating unit for interfacing the operations of the first unit with the operations of the second unit, the method comprising the steps of:synchronizing operations of the first operating unit with first clock signals; synchronizing operations of the second operating unit with second clock signals which are asynchronous with the first clock signals; nominally synchronizing operations of the third unit with the operations of the first unit; monitoring an extent of asynchrony between the operations of the second and the third units, to determine whether the extent of asynchrony lies outside of a predetermined range of allowed asynchrony; and adjusting the synchronization of the operations of the third unit with the operations of the first unit, in response to a determination that the extent of asynchrony does lie outside of the predetermined range, to move the extent of asynchrony between the operations of the second and the third units to within the range.
 25. The method of claim 24 wherein:the step of synchronizing operations of the first unit comprises the step of synchronizing the operations of the first operating unit with first timing signals having a nominal frequency and a first phase; the step of synchronizing operations of the second unit comprises the step of synchronizing the operations of the second operating unit with second timing signals having the nominal frequency and a second phase different from and fluctuating with respect to the first phase; the step of nominally synchronizing operations of the third unit comprises the step of synchronizing operations of the third operating unit with third timing signals having the nominal frequency and a third offset by an adjustably fixed amount from the first phase; the step of monitoring comprises the step of determining whether the third phase falls outside of a predetermined range of allowed offset from the second phase; and the step of adjusting comprises the step of adjusting the fixed offset of the third phase from the first phase, in response to a determination that the third phase falls outside of the predetermined range, to move the third phase to within the range.
 26. A method of operating a communications system comprising a first unit for transmitting incoming communications, a second unit for receiving incoming communications, and a third unit for interfacing communications between the first and the second units, the method comprising the steps of:transmitting incoming communication traffic from the first unit at times dictated by first clock signals having a nominal frequency and a first phase different from and fluctuating with respect to a second phase; receiving the transmitted incoming communication traffic at the third unit; transmitting from the third unit to the second unit incoming communication traffic received from the first unit at times dictated by second clock signals having nominal frequency and having a third phase that is offset by an adjustably fixed amount from the second phase; receiving incoming communication traffic transmitted from the third unit at the second unit at times dictated by third clock signals having the nominal frequency and the second phase; determining whether the third unit receives incoming communication traffic from the first unit within predetermined windows of time prior to the times of transmission by the third unit of the received incoming communication traffic; and either increasing or decreasing the amount of the offset of the third phase from the second phase, in response to a determination that receptions of the incoming communication traffic at the third unit fall outside of the windows, to move the receptions into the windows.
 27. A method of claim 26 whereinthe step of either increasing or decreasing the amount of the offset comprises the steps of: adjusting the offset at commencing of a communication in one step by any amount required to move the receptions substantially into centers of the windows; and adjusting the offset during the communication in a series of sequential steps.
 28. The method of claim 26 further comprising the steps of :inserting additional traffic into the incoming communication traffic received by the third unit transmitting the additional traffic to the second unit while the amount of the offset is being increased; and deleting a portion of the incoming communication traffic received by the third unit from the incoming communication traffic transmitted to the second unit while the amount of the offset is being decreased.
 29. A method of operating a communications system comprising a first unit for transmitting communications, a second unit for receiving outgoing communications, and a third unit for interfacing communications between the first and the second units, the method comprising the steps of:transmitting outgoing communication traffic from the first unit at times dictated by the first clock signals having nominal frequency and a first phase; receiving at the third unit the outgoing communication traffic transmitted by the first unit; transmitting from the third unit to the second unit outgoing communication traffic received from the first unit at times dictated by second clock signals having the nominal frequency and having a second phase that is offset by an adjustably fixed amount from the first phase; receiving at the second unit the outgoing communication traffic transmitted by the third unit; transmitting outgoing communication traffic from the second unit at times dictated by third clock signals having the nominal frequency and a third phase different from and fluctuating with respect to the first phase; determining whether the second unit receives outgoing communication traffic from the third unit within predetermined windows of the time prior to the times of transmission by the second unit of the received outgoing communication traffic; and either increasing or decreasing the amount of the offset of the second phase from the first phase, in the response to a determination that receptions of the outgoing communication traffic at the second unit fall outside of the windows, to move the receptions into the windows.
 30. The method of claim 29 whereinthe step of either increasing or decreasing the amount of the offset comprises the steps of: adjusting the offset at commencing of a communication in one step by any amount required to move the receptions substantially into centers of the windows; and adjusting the offset during the communication in a series of sequential steps.
 31. The method of claim 29 further comprising the steps of:inserting additional traffic into the outgoing communication traffic transmitted from the first unit causing the third unit to receive the additional traffic while the amount of the offset is being increased; and deleting a portion of the outgoing communication traffic transmitted by the first unit from the outgoing communication traffic received by the third unit while the amount of the offset is being decreased.
 32. A method of operating a communications system comprising a first unit for transmitting outgoing communication traffic and receiving incoming communication traffic, a second unit for transmitting received incoming and outgoing communication traffic, and a third unit for interfacing communications between the first and the second units, the method comprising the steps of:transmitting outgoing communication traffic from the first unit and receiving incoming communication traffic at the first unit at times dictated by first clock signals having a nominal frequency and a first phase; transmitting received incoming and outgoing communication traffic from the second unit at times dictated by the second clock signals having the nominal frequency and a second phase different from and fluctuating with respect to the first phase; receiving at the third unit the outgoing communication traffic transmitted by the first unit; transmitting from the third unit to the second unit outgoing communication traffic received from the first unit at times dictated by third clock signals having the nominal frequency and having a third phase that is offset by an adjustably fixed first amount from the first phase; receiving at the third unit the incoming communication traffic transmitted by the second unit; transmitting from the third unit to the first incoming communication traffic received from the second unit at times dictated by fourth clock signals having the nominal frequency and having a fourth phase that is offset by an adjustably fixed second amount from the first phase; determining whether the second unit receives outgoing communication traffic from the unit within first predetermined windows of the time prior to the times of transmission by the second unit of the received outgoing communication traffic; determining whether the third unit receives incoming communication traffic from the second unit within second predetermined windows of time prior to the times of transmission by the third unit of the received incoming communication traffic; and either increasing or decreasing the amount of the offset of either the third phase or the fourth phase from the first phase, in response to a determination that either receptions of the outgoing communication traffic at the second unit fall outside of the first windows or receptions of the incoming communication traffic at the third unit fall outside of the second windows, to move the receptions that fall outside of their corresponding windows into the corresponding windows.
 33. The method of claim 32 whereinthe step of either increasing or decreasing the amount of the offset comprises the step of: decreasing the amount of the offset of the third phase from the first phase, in response to a determination that receptions of the outgoing communication traffic at the second unit lag the first windows.
 34. The method of claim 33 whereinthe step of either increasing or decreasing the amount of the offset further comprises the step of: increasing the amount of the offset of the third phase from the first phase, in response to a determination that receptions of the outgoing communication traffic at the second unit lead the first windows.
 35. The method of claim 32 whereinthe step of either increasing or decreasing the amount of the offset comprises the step of: increasing the amount of the offset of the fourth phase from the first phase, in response to a determination that receptions of the incoming communication traffic at the third unit lag the second windows.
 36. The method of claim 35 whereinthe step of either increasing or decreasing the amount of the offset further comprises the step of: decreasing the amount of the offset of the fourth phase from the first phase, in response to a determination that receptions of the incoming communication traffic at the third unit lead the second windows.
 37. The method of claim 32 whereinthe step of either increasing or decreasing the amount of the offset comprises the step of: adjusting the first amount and the second amount of the offset at commencing of a communication each in one step by any amount required to move the receptions that fall outside of their corresponding windows into the corresponding windows; and adjustment the first amount and the second amount of offset during the communication in a series of sequential steps by an integral multiple of the same predetermined amount during each step.
 38. The method of claim 32 further comprising the steps of:inserting additional traffic into the outgoing communication traffic transmitted from the first unit and causing the third unit to receive the additional traffic while the amount of the offset of the third phase is being increased; deleting a portion of the outgoing communication traffic transmitted by the first unit from the outgoing communication traffic received by the third unit while the amount of the offset of the third phase is being decreased; inserting additional traffic into the incoming communication traffic received by the third unit and transmitting the additional traffic to the first unit while the amount of the offset of the fourth phase is being increased; and deleting a portion of the incoming communication traffic received by the third unit from the incoming communication traffic transmitted to the first unit while the amount of the offset of the fourth phase is being decreased.
 39. The amount of claim 32 in a communications system wherein the first unit is for transmitting a stream of outgoing communication traffic and receiving a stream of incoming communication traffic, and the second unit is for transmitting packets of received incoming communication traffic, and receiving packets of outgoing communication traffic for transmission of the outgoing communication traffic, wherein:the step of receiving at the third unit the outgoing communication traffic transmitted by the first means comprises the steps of receiving the stream of outgoing communication traffic from the first unit, and packetizing the received outgoing communication traffic; the steps of transmitting from the third unit to the second unit outgoing communication traffic comprises the step of transmitting the packets of the received outgoing communication traffic to the second unit at times dictated by the third clock signals; the step of receiving at the third unit the incoming communication traffic transmitted by the second unit comprises the steps of receiving the packets of the incoming communication traffic from the second unit, and depacketizing the received incoming communication traffic; the step of transmitting from the third unit to the first incoming communication traffic comprises the step of transmitting the depacketized received incoming communication traffic toward the first unit at times dictated by the fourth clock signals; the step of determining whether the second unit receives outgoing communication traffic comprises the step of determining whether the second unit receives the packets of outgoing communication traffic from the third unit within the first predetermined windows; and the step of determining whether the third unit receives incoming communication traffic comprises the steps of determining whether the third unit receives the packets of incoming communication traffic from the second unit within the second predetermined windows.
 40. A method of processing call traffic in an interface arrangement of a cellular radio-telephone system that includes the arrangement, at least one cell each for transmitting first packets containing first frames of coded incoming call traffic received from a radio telephone to the arrangement and for transmitting to the radio telephone outgoing call traffic received from the arrangement in second packets containing second frames of coded outgoing call traffic, and a mobile-telephone switching system for interconnecting cells with each other and with a telephone network by routing a first digital stream of incoming call traffic received from the arrangement to a destination and by routing a second digital stream of outgoing call traffic received from a source to the arrangement and wherein the first and the second digital streams are synchronized with first clock signals having a nominal frequency and a first phase and derived from the telephone network and the transmissions of the incoming and the outgoing call traffic by the cell are synchronized with second clock signals having the nominal frequency and a second phase that is different from and fluctuates with respect to the first phase, the method comprising the steps of:receiving the second digital stream of outgoing call traffic synchronously with the first clock signals; coding the received outgoing call traffic; transmitting second frames of the coded outgoing call traffic synchronously with third clock signals having the nominal frequency and a third phase that is offset by an adjustably fixed first amount from the first phase; receiving the second frames of the coded outgoing call traffic; packetizing the received second frames into the second packets; transmitting the second packets to the cell synchronously with fifth clock signals having the nominal frequency and a fifth phase that is offset by an adjustably fixed third amount from the first phase; receiving the first packets from the cell; depacketizing the received first packets into the first frames; transmitting the first frames synchronously with sixth clock signals having the nominal frequency and a sixth phase that is offset by an adjustably fixed fourth amount from the first phase; receiving the first frames of coded incoming call traffic synchronously with fourth clock signals having the nominal frequency and a fourth phase that is offset by an adjustably fixed second amount from the first phase; decoding the received incoming call traffic; transmitting the second digital stream of incoming call traffic synchronously with the first clock signals; determining whether the interface arrangement receives the first packets within first predetermined windows of time prior to the times of transmission of the first frames by the interface arrangement; determining whether the cell receives the second packets within second predetermined windows of time prior to the times of transmission by the cell of the received outgoing call traffic to the mobile telephone; and either increasing or decreasing the amounts of the offsets of either both the third and the fifth phases or both the fourth and the sixth phases, with respect to the first phase, in response to a determination that either receptions of the first packets fall outside of the first windows or receptions of the second packets fall outside of the second windows, to move the packet receptions that fall outside of their corresponding windows into the corresponding windows.
 41. The method of claim 40 whereinthe step of either increasing or decreasing the amounts of the offsets comprises the step of: increasing the amounts of the offsets of both the fourth and the sixth phases from the first phase by a same amount, in response to a determination that receptions of the first packets at the interface arrangement lag the first windows.
 42. The method of claim 41 whereinthe step of either increasing or decreasing the amounts of the offsets further comprises the step of: decreasing the amounts of the offsets of both the fourth and the sixth phases from the first phase by a same amount, in response to a determination that receptions of the first packets at the interface arrangement lead the first windows.
 43. The method of claim 40 whereinthe step of either increasing or deceasing the amounts of the offsets comprises the step of: decreasing the amounts of the offsets of both the third and the fifth phases from the first phase by a same amount, in response to a determination that receptions of the second packets at the cell lag the second windows.
 44. The method of claim 43 whereinthe step of either increasing of decreasing the amounts of the offsets further comprises the step of: increasing the amounts of the offsets of both the third and the fifth phases from the first phase by a same amount, in response to a determination that receptions of the second packets at the cell lead the second windows.
 45. The method of claim 40 whereinthe step of either increasing or decreasing the amounts of the offsets comprises the steps of: adjusting either the first and the third amounts of offset or the second and the fourth amounts of offset, in one step by any amount required to move any packet receptions that fall outside of their corresponding windows into the corresponding windows at a commencing of a communication; and adjusting either the first and the third amounts of offset or the second and the fourth amounts of offset by an integral multiple of a same predetermined amount in each step of a series of sequential steps to move packet receptions that fall outside of their corresponding windows into the corresponding windows during the communication.
 46. The method of claim 40 further comprising the steps of:inserting traffic additional to the outgoing call traffic into the second frames while the amounts of the offsets of the third and the fifth phases are being increased; deleting a portion of the outgoing call traffic from the second frames while the amounts of the offsets of the third and the fifth phases are being decreased; inserting traffic additional to the incoming call traffic into the first digital stream while the amounts of the offsets of the fourth and the sixth phases are being increased; and deleting a portion of the incoming call traffic from the first digital stream while the amounts of the offsets of the fourth and the sixth phases are being decreased. 